Find out about intrauterine (artificial) insemination, or IUI, a fertility treatment that involves directly inserting sperm into a woman's womb.
Read 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 widespread and persistent thick, dry, "fish-scale" skin.
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 (IBD), which is a term mainly used to describe 2 conditions: Crohn's disease and ulcerative colitis.
Read about ingrown hairs, including what causes them and advice about what to do if you have them.
Read about an ingrown toenail, which develops when the sides of the toenail grow into the surrounding skin.
Find out about intensive care units (ICUs), specialist hospital wards for people who are seriously ill.
Read about interstitial cystitis, a long-term painful bladder condition. Find out what the symptoms are, what might cause it, and what treatments are available.
Find out what intracranial hypertension (IH) is, what the symptoms are, why it happens, and how it's treated.
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 substance in the blood and urine.
Find out about idiopathic pulmonary fibrosis (IPF), including what the symptoms are, how it's treated and what the outlook is.
An ileostomy is where the small bowel (small intestine) is diverted through an opening in the tummy (abdomen).
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 occurs when an internal part of the body pushes through a weakness in the muscle or surrounding tissue wall.
Read about some of the most common insect bites and stings, how they're treated and when to get medical advice.
Read about insomnia, including why it might happen and how to treat it.
Read 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 what causes irregular periods, when to see your 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, a symptom that gives you a strong urge to scratch the skin around your anus. Find out how to ease the itching and when to see a GP.
Itchy skin is not usually a sign of anything serious. You can often treat it yourself and it will usually go away after a few weeks.
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.