A bunion
A bunion is a bump or lump at the base of the big toe. Although arthritis in the big toe joint (hallux rigidus) can produce a bunion-like lump on the top of the joint (so called dorsal bunion), the term bunion is usually reserved for the side bump which results from the big toe angling towards the second toe (hallux valgus). The arthritic bump (osteophyte) of hallux rigidus is a spur of bone which blocks movement and is usually accompanied by a stiff, achy big toe joint. Osteophytes sometimes become truly enormous and can cause the skin to ulcerate even if the joint itself is not particularly painful.
True bunions (hallux valgus) are caused by the base of the big toe being thrust sideways as the toe itself tilts in the opposite direction towards the second toe ("index" toe as in index finger). The index toe can become elevated and the big toe cross beneath. Painful callosities form beneath the ball of the index and middle toes which can become increasingly clawed. Large bunions of any sort can even cause the skin to ulcerate but if they are exceptionally inflamed, conditions such as gout or rheumatoid arthritis should be considered.