Diseases & Conditions
Quick reference for almost any health condition
MedlinePlus – A service of the U.S. National Library of Medicine
Herrick Library Reliable Sources of Health Information
MedlinePlus – A service of the U.S. National Library of Medicine
Herrick Library Reliable Sources of Health Information
Arthritis Foundation – Information on the more than 100 types of arthritis and related conditions, as well as treatment options and other resources for living with arthritis. For quick assistance, visit the Health & Wellness page. Información sobre artritis en Español.
Centers for Disease Control and Prevention (CDC): Arthritis – Government website covering all aspects of arthritis care, including risk factors, medications, and what type of physical activities are helpful. Información sobre artritis en Español.
The Johns Hopkins Arthritis Center – Arthritis information from one of the largest hospitals in the United States. Includes information and videos on specific types of arthritis and current information for managing and treating arthritis in the Patient Corner.
National Institute of Arthritis and Musculoskeletal and Skin Diseases – One of the National Institutes of Health, NIAMS researches and provides information on diseases and treatment of the bones, joints, muscles, and skin. Información del Instituto Nacional de Artritis y Enfermedades Musculoesqueléticas y de la Piel en Español.
OrthoInfo: American Academy of Orthopaedic Surgeons – Information on all joints and bones. Includes sections on diseases and conditions, treatment and surgeries, prevention and safety, broken bones and injury sections, and joint replacement. Includes videos and multimedia resources. Información sobre ortopaedia (el sistema músculo-esquelético) en Español.
Alzheimer’s Association – Works on a global, national, and local level to provide care and support for those affected by Alzheimer’s and other dementias. Website provides extensive information as well as Life with Alzheimer’s, help resources, and the San Diego/Imperial County Chapter. Información sobre Alzheimer y demencia en Español. Click the Languages box on the home page for information in 5 other languages.
Alzheimers.gov – Operated by the Department of Health and Human Services, this site provides information about what Alzheimer’s and other dementias are, treatment options, how to pay and plan, caring for someone, and support and help resources. Información sobre Alzheimer y demencia en Español.
Alzheimer’s San Diego – Locally-operated nonprofit organization that provides San Diego families with support, information, and resources. Website includes extensive links to Programs and Resources and information on Alzheimer’s and dementia.
American Brain Tumor Association – Tumor and treatment information, care and support, and tumor research are some of the topics covered. Includes comprehensive information on many different types of brain tumors, including those in children.
Brain health: National Institute on Aging – Operated by the National Institute on Aging, this site provides information about changes to the brain from Alzheimer’s and various related dementias. For other brain disorders see Disorders A – Z. Información sobre Alzheimer y demencia en Español.
National Institute of Neurological Disorders and Stroke – One of the National Institutes of Health, NINDS provides information on hundreds of conditions relating to the head, brain, and nervous system. Information on specific conditions may be found in the All Disorders section and in the Patient & Caregiver Education section. Página principal del Instituto Nacional de Trastornos Neurológicos y Accidentes Cerebrovasculares en Español y Publicaciones en Español.
American Cancer Society – Information about all types of cancer, treatment, research, and staying healthy. Información sobre el cáncer y la prevención en Español. Click here for information in 13 other languages.
National Cancer Institute – One of the National Institutes of Health, NCI provides information on all types of cancer, diagnosis, treatment, clinical trials, and other cancer topics. Información del Instituto Nacional del Cáncer en Español.
Bladder Cancer Advocacy Network – BCAN works to increase public awareness about bladder cancer, to advance bladder cancer research, and to provide educational and support services for the bladder cancer community.
Breastcancer.org – Nonprofit organization that provides information on all aspects of breast cancer including symptoms and diagnosis, treatment options and side effects, help with lymphedema, and understanding risk factors. Información sobre el cancer de mama en Español.
Colon and Rectal Cancer – The American College of Colon and Rectal Surgeons has information for patients about colorectal conditions, screenings, and treatments.
Leukemia and Lymphoma Society – Nonprofit organization that provides information, education, and support for all types of blood cancers. Información en Español.
GO2 Foundation for Lung Cancer – A national non-profit organization dedicated to patient support and advocacy for people living with lung cancer and those at risk for the disease.
Melanoma (Skin Cancer) – The American Academy of Dermatology provides information for the public on melanoma’s signs, symptoms, diagnosis, and treatment. Cáncer de Piel en Español.
Prostate Cancer Foundation – Detailed information on all aspects of prostate cancer including symptoms, diagnosis, and treatment, and specifically information for patients.
Eunice Kennedy Shriver National Institute of Child Health and Human Development – This site contains research-based information and resources related to the health of children, adults, families, and communities. Includes A-Z Health and Research Topics with information on childhood diseases. Información del Instituto Nacional de la Salud Infantil y Desarrollo Humano en Español.
FamilyDoctor.org – The American Academy of Family Physicians provides information on Diseases and Conditions, Prevention and Wellness, and Family Health for all ages. Información de la Academia Americana de Médicos de Familia en Español.
Healthy Children – The American Academy of Pediatrics provides extensive information on health and wellbeing for children and families. Información sobre la salud de niños y familias en Español.
KidsHealth – As part of The Nemours Foundation’s Center for Children’s Health Media, this site provides families with information, perspective, advice, and comfort about a wide range of physical, emotional, and behavioral issues that affect children and teens. Separate sections for Kids, Teens, and Parents.
American Diabetes Association – Extensive information on all types of diabetes and diagnosis, treatment, prevention, diet, and fitness. Audio option available on most pages to listen to the text. Información de la Asociación Americana de la Diabetes en Español.
American Heart Association: Diabetes – Discusses diabetes, symptoms, risk, how to maintain health with diabetes, and its relationship to heart problems.
National Institute of Diabetes and Digestive and Kidney Diseases – One of the National Institutes of Health, NIDDK provides in-depth information on diabetes and its diagnosis, prevention, treatment, complications, and effect on other health conditions. NIDDK sponsors the National Diabetes Education Program. Información del Instituto Nacional de la Diabetes y las Enfermedades Digestivas y Renales sobre la diabetes en Español.
American College of Gastroenterology – The ACG provides a Patient Education & Resource Center with information on gastrointestinal and digestive diseases. Also provides video and audio podcasts on a variety of conditions and topics. Recursos del Colegio Americano de Gastroenterología en Español.
International Foundation for Functional Gastrointestinal Disorders – IFFGD provides detailed information and resources on a wide range of digestive conditions and diseases.
National Institute of Diabetes and Digestive and Kidney Diseases – One of the National Institutes of Health, NIDDK provides in-depth information on digestive diseases, awareness, prevention, symptoms, and treatment. Información del Instituto Nacional de la Diabetes y las Enfermedades Digestivas y Renales sobre las enfermedades digestivas en Español.
Please visit the Disability Resources page on our website by clicking here.
American Optometric Association – Detailed information on all aspects of eye health, including eye and vision problems, good vision throughout life, and caring for your vision.
BrightFocus® Foundation – Contains extensive information and links to resources on Alzheimer’s disease, macular degeneration, and glaucoma. Información sobre la enfermedad de Alzheimer, el glaucoma, y la degeneración macular en Español.
EyeSmart – The American Academy of Ophthalmology sponsors this comprehensive site on all aspects of eye care, diseases and conditions, and symptoms. Includes Eye Health A-Z. Informacion del sitio OjosSanos sobre la salud ocular en Español.
National Eye Institute – One of the National Institutes of Health, the NEI supports programs and research relating to eye diseases, visual disorders, preservation of sight, and health problems and requirements of the blind. Includes A-Z Diseases and Disorders and a comprehensive photo, image, and video library. NEI sponsors the National Eye Health Education Program and the NEI for Kids website for children. Información del Instituto Nacional del Ojo en Español.
American Academy of Otolaryngology – Head and Neck Surgery – Health Information section provides an overview of diagnoses and treatment for diseases and disorders of the ears, nose, throat, head, and neck. Includes information on cancer as well as common ailments in children.
MedlinePlus – A service of the U.S. National Library of Medicine and the National Institutes of Health, MedlinePlus provides information and resources on Head Injuries, Neck Injuries and Disorders, Ear Disorders, Nose Injuries and Disorders, and Throat Disorders. Información en Español: Lesiones en la Cabeza, Lesiones y Enfermedades del Cuello, Enfermedades del Oído, Lesiones y Enfermedades de la Nariz, y Enfermedades de la Garganta.
AARP: Health – Information on healthy living, Medicare, conditions and treatments, drugs and supplements, health insurance, and brain health. Información de salud en Español.
National Institute on Aging: Physical Activity – Exercise and physical activity information for older adults from the National Institute on Aging. Site offers exercises, motivational tips, and free resources including an exercise guide.
Healthy for Good™ – This initiative from the American Heart Association includes tips on healthy eating, physical activity, weight management, stress management, quitting smoking, workplace health, and keeping kids healthy.
Healthy Living – Information from the Centers for Disease Control and Prevention (CDC) on a variety of health and wellness topics, tips for staying healthy, and healthy living by life stages. Información de los Centros para el Control y la Prevención de Enfermedades sobre la vida saludable en Español.
HHS.gov – The U.S. Department of Health and Human Services provides information on many topics relating to children and adolescents. The HHS website contains information for all ages about immunizations, the environment, nutrition, mental health, healthy lifestyle, and exercise.
American Hearing Research Foundation – Provides information on numerous hearing disorders and balance disorders.
Association of Late-Deafened Adults – Provides information, support, and resources for people who have lost the ability to understand speech with or without hearing aids after acquiring spoken language.
Better Hearing Institute – Provides brief information and resources on hearing loss in adults and children, treatments, and prevention.
National Institute on Deafness and Other Communication Disorders – One of the National Institutes of Health, NIDCD provides information on hearing, ear infections, deafness, balance, smell and taste, and voice, speech and language. Includes an A-Z index. Información del Instituto Nacional de la Sordera y Otros Trastornos de la Comunicación en Español.
Vestibular Disorders Association – Provides information on the vestibular system, which includes the parts of the inner ear and brain that process the sensory information involved with controlling balance and eye movements. If disease or injury damages these processing areas, problems with balance, dizziness, or other medical conditions can result.
If someone may be having a heart attack, call 911.
Si sospecha que alguien esta teniendo un ataque al corazón, llame al 9-1-1 inmediatamente.
American Heart Association – Detailed information on many heart and cardiovascular conditions as well as related conditions. Also provides information on healthy living and support.
Heart Attack Signs (NHLBI) – Information and a video on heart attack warning signs, heart attack survival, testing for a heart attack, and reducing the risk of heart attack. Síntomas de un ataque al corazón en Español.
National Heart, Lung, and Blood Institute – NHLBI is one of the National Institutes of Health and provides health information for the public on all heart, lung, and blood diseases and conditions, including sleep disorders. Provides an A-Z index. Temas de salud del Instituto Nacional del Corazón, los Pulmones y la Sangre en Español.
Women’s Heart Foundation – Discusses heart care from a women’s perspective and explains how heart disease symptoms present differently in women than in men.
AIDS.org – Provides education and information to help prevent HIV infections and to improve the lives of those affected by HIV and AIDS.
HIV.gov – The U.S. Department of Health and Human Services provides information on all aspects of HIV/AIDS, including prevention, treatment, staying healthy, and where to find care and treatment. (Website was formerly called AIDS.gov)
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention – Part of the Centers for Disease Control and Prevention (CDC), the National Center provides patient education resources and links to other sites. El VIH y los hispanos o latinos en Español.
Office of AIDS Research – Part of the National Institutes of Health, OAR provides links to HIV/AIDS information and resources, particularly from other NIH centers and other government health agencies.
American Association of Kidney Patients (AAKP) – Nonprofit patient organization that provides information on chronic kidney disease, dialysis, transplant, and Fabry Disease, as well as information for parents of children with kidney illness and links to support groups. The AAKP store contains brochures and pamphlets that can be downloaded for free.
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) – Part of the National Institutes of Health, NIDDK provides in-depth information on kidney and urologic diseases, awareness and prevention, and treatment and complications. Información sobre las enfermedades urológicas y de los riñones en Español.
National Kidney Disease Education Program (NKDEP) – NKDEP is an initiative of the National Institutes of Health to raise awareness about kidney disease. Provides information about testing for kidney disease, how to keep your kidneys healthy, living with kidney disease, talking to your doctor, and talking to your family. Includes Kidney Disease topics and conditions.
National Kidney Foundation – Information on all aspects of kidney health, kidney disease, prevention and early detection of disease, treatments, and organ donation and transplantation. Información sobre los riñones en Español.
Urology Care Foundation – The American Urological Association provides patient information on conditions and treatments, including bladder, kidney, adrenal glands, prostate, and cancer. Educational materials can be downloaded for free.
American Lung Association – Provides information on how the lungs work, how to protect your lungs, and lung diseases, including asthma, COPD, pneumonia, cancer, and many others. Includes information on support groups and quitting smoking. Información sobre las enfermedades pulmonares en Español.
National Heart, Lung, and Blood Institute – One of the National Institutes of Health, NHLBI provides information for the public on a wide range of lung diseases. Health Topics A – Z.
Please visit the Drugs, Herbs, and Vitamins page on our website by clicking here.
FDA (U.S. Food and Drug Administration) – Regulates and controls prescription medications and dietary supplements in the U.S. Includes information on Pharmacy Compounding and Medical Devices. Información de la Administración de Medicamentos y Alimentación en Español.
MedlinePlus Drug Information – A service of the U.S. National Library of Medicine and the National Institutes of Health, MedlinePlus provides information on side effects, dosage, and special precautions of prescription drugs and over-the-counter medicines as well as the effectiveness, usual dosage, and drug interactions of herbs and supplements. Información sobre medicinas, hierbas, y suplementos en Español.
MedlinePlus: Men’s Health – A service of the U.S. National Library of Medicine and the National Institutes of Health, MedlinePlus provides information on a wide range of men’s health issues. Click here for a list of common conditions. Información sobre la salud de los hombres en Español. Temas de salud de los hombres.
National Center for Complementary and Integrative Health – The NCCIH is part of the National Institutes of Health and provides resources and information on health conditions of special concern to men. It also includes summaries of research on the effects of complementary health approaches in men with certain conditions.
In addition to the following links to Mental Health resources, the Herrick Library subscribes to these relevant magazines:
• BP (Bipolar)
• Mind, Mood & Memory (newsletter)
• Mindful: Taking Time for What Matters
• Psychology Today
• Scientific American (includes Scientific American MIND)
• Spirituality & Health
• Vibrant Life
MentalHealth.gov – Provides one-stop access to U.S. government mental health information for the general public and others. Includes information on specific mental health conditions, information for specific groups, and how to get help. Información sobre la salud mental en Español.
NAMI: National Alliance on Mental Illness – Provides easy-to-understand information about mental illness, mental health care, diagnosis, treatment, support, and recovery. Información de la Alianza Nacional de Enfermedades Mentales sobre la Salud Mental en la Comunidad Latina en Español.
National Institute of Mental Health – One of the National Institutes of Health, NIMH provides information on a variety of mental health topics, treatments, and information by age/gender. Información sobre las enfermedades mentales en Español.
National Suicide Prevention Lifeline – Information on getting help with depression and other mental issues. Dialing 988 provides free and confidential emotional support to people in suicidal crisis or emotional distress, 24 hours a day, 7 days a week, across the U.S. 988 has been designated as the new (July 2022) three-digit dialing code. When people call, text, or chat 988 they will be connected to trained counselors that are part of the existing National Suicide Prevention Lifeline network. The current Lifeline phone number: 1-800-273-8255 will remain available. Lifeline for the deaf or hard of hearing TTY: 1-800-799-4889. Ayuda de la Red Nacional de Prevención del Suicidio en Espanol. Ofrece 24/7 gratuito servicios en Español: 1-888-628-9454.
Substance Abuse and Mental Health Services Administration – Part of the U.S. Department of Health and Human Services, SAMHSA promotes mental health and implements prevention and early intervention strategies to reduce the impact of mental illness and substance abuse. SAMHSA National Helpline is a free, confidential, 24/7 treatment referral and information service in English or Español: 1-800-662 HELP (4357).
Teen Line – Providing confidential peer support for young people, this teen-to-teen helpline is affiliated with Cedars-Sinai Medical Center in Los Angeles, California. TEEN LINE is staffed by trained teen listeners who handle telephone calls, texts, and emails concerning a wide variety of subjects including suicide, rape, child abuse, addictions, family problems, and relationship conflicts. Operates every evening from 6:00 p.m. to 10:00 p.m. PST. Toll free in California 1-800-852-8336 or nationwide 1-310-855-4673. Text “TEEN” to 839863.
American Chronic Pain Association – Facilitates peer support and education for individuals with chronic pain and their families. Includes Conditions A to Z, treatments, pain management tools, and clinical trials.
Institute for Chronic Pain – Offers information about understanding chronic pain, treating chronic pain, and common conditions associated with chronic pain.
National Institutes of Health Pain Consortium – The NIH Pain Consortium enhances research and promotes collaboration across many NIH institutes and centers that have programs addressing pain. Includes an A-Z index to various NIH brochures and information about pain symptoms, conditions, and treatments. Información en Español.
Health Physics Society – This nonprofit organization of radiation safety professionals provides public information on radiation, radioactive materials, and radiation safety, including their use for medical diagnosis and therapy.
RadiologyInfo.org – The American College of Radiology provides this patient website to explain how x-ray, CT, MRI, ultrasound, radiation therapy and other procedures are performed. The Procedures A to Z index contains over 200 procedure and exam descriptions, including how to prepare and what you may experience. Información sobre radiología para pacientes en Español.
Genetic and Rare Diseases Information Center (GARD) – GARD is a program of the National Institutes of Health’s National Center for Advancing Translational Sciences. It provides the public with access to current, reliable, and easy-to-understand information about rare or genetic diseases. A rare disease is defined (in the United States) as a condition that affects fewer than 200,000 people. Browse the A-Z List of over 6,500 rare diseases. Información del Centro de Información sobre Enfermedades Genéticas y Raras en Español.
National Organization for Rare Disorders (NORD) – Nonprofit patient advocacy organization that provides services for patients and their families, rare disease patient organizations, medical professionals, and those seeking to develop new diagnostics and treatments. Section for Patients and Families includes information and resources, A-Z list of rare diseases, help to access medications, and links to patient organizations. Requires free registration to access full reports.
AARP: Health – Includes information on conditions and treatments, brain health, drugs and supplements, and insurance and Medicare, all geared for seniors. The site is also a good resource for general information pertaining to senior issues. Información de salud en Español.
Bright Focus® Foundation – Contains extensive information and links to resources on Alzheimer’s disease, macular degeneration, and glaucoma. Información sobre la enfermedad de Alzheimer, el glaucoma, y la degeneración macular en Español.
HealthinAging.org – The American Geriatrics Society provides consumers and caregivers with up-to-date information on health and aging, including Aging & Health A-Z and finding a healthcare professional who specializes in caring for older adults.
Healthy Aging (Centers for Disease Control and Prevention) – Provides thorough information on health and aging topics, including the Healthy Brain Initiative, mental health and aging, advance care planning, and more.
National Institute on Aging – One of the National Institutes of Health, NIA provides information on healthy aging, caregiving, medications, and diseases. Site includes Health Topics A-Z as well as links to hundreds of health and aging organizations. Publicaciones del Instituto Nacional Sobre el Envejecimiento en Español.
American Academy of Dermatology – Features a Diseases and Conditions section that lists dozens of skin conditions and problems and offers insights into the care and treatment of your skin, hair and nails.
American Skin Association – The ASA works to advance research and provide information on skin health, disorders, and diseases, including melanoma and other skin cancers. Includes information on sun safety and information specifically for children.
National Institute of Arthritis and Musculoskeletal and Skin Diseases – One of the National Institutes of Health, NIAMS researches and provides information on diseases of the bones, joints, muscles, and skin. Información del Instituto Nacional de Artritis y Enfermedades Musculoesqueléticas y de la Piel en Español.
National Heart, Lung and Blood Institute – One of the National Institutes of Health, NHLBI provides information and easy-to-read fact sheets on sleep and sleep disorders including insomnia, restless legs syndrome, narcolepsy, sleep apnea, and a guide to healthy sleep.
National Institute of Neurological Disorders and Stroke – One of the National Institutes of Health, NINDS provides information on understanding sleep, including tips for a good night’s sleep. Site covers comprehensive information on sleep disorders such as apnea, restless legs syndrome, and narcolepsy. Publicaciones sobre el sueño en Español.
SleepEducation.com – The American Academy of Sleep Medicine provides this site for patients and the public and covers all aspects of sleep, including how to evaluate if you sleep well, sleep disorders, treatments, and how to find a professional to help you.
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention – Part of the Centers for Disease Control and Prevention (CDC), the National Center provides extensive patient education resources and links to other sites.
National Institute of Allergy and Infectious Diseases – One of the National Institutes of Health, NIAID provides information on all types of sexually transmitted diseases.
If someone may be having a stroke, call 911.
Si sospecha que alguien esta teniendo un ataque cerebral, llame al 9-1-1 inmediatamente.
American Stroke Association – The American Stroke Association provides information about stroke, life after stroke, and warnings signs of stroke. Call 9-1-1 if you think someone might be having a stroke. Recursos sobre el ataque cerebral en Español. Si sospecha que alguien esta teniendo un ataque cerebral, llame al 9-1-1 inmediatamente.
National Institute of Neurological Disorders and Stroke – One of the National Institutes of Health, NINDS includes information about what strokes are, questions and answers about stroke, and how to prevent strokes.
Alcoholics Anonymous – AA is a well-known organization dedicated to members helping each other in their recovery from alcoholism. Open to anyone who wants to do something about their drinking problem. Información sobre Alcohólicos Anónimos en Español.
National Institute on Alcohol Abuse and Alcoholism – One of the National Institutes of Health, NIAAA contains information, resources, publications, links to support and treatment, and information for special populations and co-occurring disorders. Publicaciones sobre el alcoholismo en Español.
National Institute on Drug Abuse – One of the National Institutes of Health, NIDA provides information on drug abuse for students and young adults, parents and teachers, and the general public. Includes descriptions of the common drugs of abuse, as well as publications, resources for help, and links to other sites. Información sobre las drogas de abuso en Español.
Office on Smoking and Health – This Centers for Disease Control and Prevention (CDC) site aids people trying to Quit Smoking including community resources and tips for quitting. Also provides basic information on the health effects of smoking, second-hand smoke, smokeless products, and more.
Partnership to End Addiction – Nonprofit organization provides support and guidance to families struggling with a child’s substance use. Provides information on the prevention of drug and alcohol use, intervention with the drug user, and finding treatment and recovery. The Drug Guide includes comprehensive information on more than 40 commonly-abused drugs and substances. Información en Español.
Smokefree.gov – Created by the Tobacco Control Research Branch of the National Cancer Institute, this site provides free, accurate, evidence-based information and professional assistance to help support the immediate and long-term needs of people trying to quit smoking. Provides information, resources, tools, and tips on quitting smoking and staying smokefree. SmokefreeEspañol para informacion y ayuda sobre dejar de fumar.
Substance Abuse and Mental Health Services Administration – Part of the U.S. Department of Health and Human Services, SAMHSA addresses drug/alcohol/tobacco use as well as mental health issues. Provides information on conditions and disorders, substances, treatment, prevention, and recovery.
Centers for Disease Control and Prevention: Vaccines & Immunizations – Answers basic and common questions on vaccines, provides information on vaccine schedules, side effects and safety, and regulations and laws. Information for parents and travelers. Resources available for specific age groups including infants, children, teens, college students, and adults.
Flu.gov – The Centers for Disease Control and Prevention (CDC) provides one-stop access to information on seasonal and other types of flu. Includes tips on flu prevention, symptoms and diagnosis, and treatment. Información sobre la influenza (gripe) en Español.
Vaccines.gov – The National Vaccine Program Office of the U.S. Department of Health and Human Services sponsors this site which provides information on vaccines and immunizations for infants, children, teens, adults, and seniors. Provides information on 22 diseases covered by vaccines as well as links to resources from other federal websites for the general public. Información sobre las vacunas en Español.
HealthyWomen – Nonprofit site covering comprehensive, objective, research-based information. Topics include pregnancy and parenting, sex and relationships, healthy living, healthy aging, and diseases and conditions.
Womenshealth.gov – The Office on Women’s Health at the U.S. Department of Health and Human Services sponsors this site which provides easy-to-understand information on a wide range of topics of interest to women. Includes A-Z Health Topics. Información de la Oficina para la Salud de la Mujer en Español.
The National Center for Complementary and Integrative Health – The NCCIH is part of the National Institutes of Health and provides resources and information on health conditions of special concern to women. It also includes summaries of research on the effects of complementary health approaches in women with certain conditions.