The lichens are skin diseases
belonging to the group of dermatoses which may also affect
the mucous membranes
, body tissue covering the inside of organs. There are several types of lichens, the most common being the "lichen planus
" and "lichen sclerosus
." The causes of these two diseases - such as those of several other lichens - are not yet known with certainty. Most often, a lichen is manifested by the appearance of small, elevated lesions
on the skin called papules, as well as a certain degree of skin thickening. Itching may also occur. Treatment depends on the type of lichen.