Find out about intrauterine (artificial) insemination, or IUI, a fertility treatment that involves directly inserting sperm into a woman's womb.
Find out about the symptoms of an infected piercing, including what to do if your piercing is infected and how to keep your piercing clean to stop it getting infected.
Find out about ichthyosis, a condition that causes dry scaly skin, including when to get medical help, treatment options and types.
Find out about indigestion, a common problem that causes pain or discomfort in your upper abdomen (dyspepsia) or behind your breastbone (heartburn).
Find out about inflammatory bowel disease, what the symptoms are, how it’s treated, what causes it and where you can get support.
Find out about ingrown hairs, what the symptoms are, how you can treat and prevent them yourself, and what treatments you can get from your GP.
NHS information about ingrown toenail, including symptoms, self-care, when to see a GP, medical treatments and prevention.
Find out about intensive care units (ICUs), specialist hospital wards for people who are seriously ill.
Intracranial hypertension is a build-up of pressure around the brain. It can cause severe headaches and problems with your vision.
Isovaleric acidaemia (IVA) is a rare, but potentially serious, inherited condition. It means the body can’t process the amino acid leucine. This causes a harmful build-up of this substance in blood and urine.
Find out about idiopathic pulmonary fibrosis (IPF), including what the symptoms are, how it's treated and what the outlook is.
Find out about impetigo, a skin infection that's very contagious but not usually serious. Read about the symptoms and when to get medical help, plus how it can be treated and prevented.
Find out about infertility, including the causes, treatment options, and when to get help and advice.
A hernia happens when an internal part of the body pushes through a weakness in the muscle or surrounding tissue wall.
Find out about some of the most common insect bites and stings, how to treat them and when to get help.
Find out about insomnia, including why it might happen and how to treat it.
Find out more about iron deficiency anaemia, including what the symptoms are, when to get medical help, the tests and treatments you may have, and the possible causes.
Find out how to check if your periods are irregular, what can cause irregular periods, when to see a GP and how irregular periods can be treated.
Read about irritable bowel syndrome (IBS) and how to treat the symptoms, which include stomach cramps, bloating, diarrhoea and constipation.
Read about itchy bottom, which is a strong urge to scratch the skin around your anus. Find out how to ease itching and when to get medical help.
Itchy skin is not usually a sign of anything serious. Find out how to treat it yourself, what medical treatments are available and what can cause it.
In vitro fertilisation (IVF) is one of several techniques available to help people with fertility problems have a baby. During IVF, an egg is removed from the woman's ovaries and fertilised with sperm in a laboratory.
Find information about ileostomy, an operation to bring the end of your small bowel to the outside of your tummy to form a stoma, including why it’s done, what happens, recovery, possible complications and what to expect after the operation.
Find out how to use internal condoms, sometimes called female condoms, to help prevent pregnancy and reduce the risk of sexually transmitted infections (STIs).
Find out about an IUD (intrauterine device) or copper coil, including who can use it, how well it works and possible side effects.