This sounds like a form of
handHand or foot spasms
Hand tremor dermatitis, called dyshydrotic eczema. Usually this is related to contact with allergens or irritants, such as soap. Infection, especially with fungal organisms, can cause a similar picture as you suggest in your note. Topical steroid ointments or emollients are commonly used to treat this condition. Vinyl gloves should be worn whenever possible. You son may have to be seen by a dermatologist.