The propensity of most autoimmune diseases to manifest themselves in the skin may result from faulty teaching of what is 'self' by epithelial cells in the thymus. Whether T cells learn what is 'self' in the thymus or not until later, peripheral to the thymus, may explain the wide range of severity of autoimmune diseases. Also, I suggest that lichen planus, alopecia areata, vitiligo and psoriasis, as well as sarcoidosis and granuloma annulare are autoimmune in nature.