According to the TheFreeDictionary's Medical dictionary, “a bunion is an abnormal enlargement of the joint (the first metatarsophalangeal joint, or MTPJ) at the base of the great or big toe (hallux). It is caused by inflammation and usually results from chronic irritation and pressure from poorly fitting footwear.”
Bunions also run in the family but it is important to note that it is not the bunion which is hereditary but the foot type. People who are flat footed are more likely to develop a bunion than those with high arches. I think this is why I developed one on my right foot at the age of 16 despite always wearing well fitted shoes – I have flat (ish) feet and my grandmother has bunions too. Other causes include leg length discrepancies, trauma to the joint, and bone displacement (hallux valgus). There is also more chance of developing a bunion as you get older.
From a Reflexology point of view, Bunions are an indication of congestion along the spleen/pancreas meridian which starts on the outer edge of both big toes. From the big toe, it runs up the leg, up through the pelvis and abdomen, and ends at the shoulder. Congestion in this meridian can also cause fungus, stiffness, and ingrowing toenails especially on the big toe; shinbone, knee, and thigh pain; varicose veins, psoriasis and eczema particularly on the legs along the meridian; groin pain and hernias; menstrual problems and other gynaecological problems such as infections, fibroids, and cysts; abdominal pain; problems in the underarm area such as eczema and lymph node swelling; and breast problems such as tenderness and lumps.
The reflex points at which a bunion occurs are the thyroid and thoracic spine. The internal branch of the spleen/pancreas meridian runs through the throat and thyroid reinforcing the bunions connection to the thyroid gland.
One of the reflexology books I own (The complete illustrated guide to reflexology by Inge Dougans) says "Most people with bunions also have problems along the spleen/pancreas meridian or pancreatic disorders, such as problems related to sugar metabolism such as a sweet tooth; cravings for stimulants such as tea, coffee, cigarettes, and alcohol; and constant hunger."
There is no specific reflex for the big toe to help relieve bunions, but massage on and around the affected area can help to relieve any pain or discomfort felt and to help reduce any inflammation in the joint. I would work on the sacral and lumbar areas of the spine reflex as these areas of the spine supply nerves to the big toe (from the lumbar and sacral nerve plexuses) and the kidney reflexes to ensure that the kidneys are functioning properly ridding the body of uric acid (this can build up in the joints especially the big toe causing gout which is a form of arthritis. Arthritis can contribute to or result from bunions). I’m sure working the leg/knee/hip reflexes would also help the condition. To help balance the spleen/pancreas meridian, I would work on the pancreas and spleen reflexes.
An interesting article on the relationship between bunions, sugar, and the spleen can be found on the Acupuncture Today website. Another interesting site about bunions is The Bunion Experiment - One woman's search for bunion cures.