Callosities and corns
Both are responses to pressure. A callosity is a more diffuse type of thickening of the keratin layer, which seems to be a protective response to widely applied repeated friction or pressure. Callosities are often occupational; e.g. they are seen on the hands of manual workers. Usually painless, they need no therapy.
Corns have a central core of hard keratin, which can hurt if forced inwards. They appear where there is high local pressure, often between bony prominences and shoes. Favourite areas include the backs of the toe joints, and the soles under prominent metatarsals. ‘Soft corns’ arise in the third or fourth toe clefts when the toes are squeezed together by tight shoes; such corns are often macerated.
The main differential is from hyperkeratotic warts, but these will show tiny bleeding points when pared down, whereas a corn has only its hard compacted avascular core surrounded by a more diffuse thicken-ing of opalescent keratin.
The right treatment for corns is to eliminate the pressure that caused them, but patients may be slow to accept this. While regular paring reduces the symp-toms temporarily, well-fitting shoes are essential. Corns under the metatarsals can be helped by soft spongy soles, but sometimes need orthopaedic alteration of weight bearing. Especial care is needed with corns on ischaemic or diabetic feet, which are at greater risk of infection and ulceration.