Cheilitis is a medical condition characterized by inflammation of the lips. The inflammation may include the perioral skin (the skin around the mouth), the vermilion border, or the labial mucosa. The skin and the vermilion border are more commonly involved, as the mucosa is less affected by inflammatory and allergic reactions.Cheilitis is a general term, and there are many recognized types and different causes. According to its onset and course, cheilitis can be either acute or chronic. Most cheilitis is caused by exogenous factors such as dryness (chapping) and acute sun exposure. Allergic tests may identify allergens that cause cheilitis. Chapped lips
Chapped lips (also known as cheilitis simplex or common cheilitis) is characterized by the cracking, fissuring, and peeling of the skin of the lips, and is one of the most common types of cheilitis. While both lips may be affected, the lower lip is the most common site. There may also be burning or the formation of large, painful cracks when the lips are stretched. Chronic cheilitis simplex can progress to crusting and bleeding. Counterintuitively, constant licking of the lips causes drying and irritation, and eventually the mucosa splits or cracks. The lips have a greater tendency to dry out in cold, dry weather. Digestive enzymes present in the saliva may also irritate the lips, and the evaporation of the water in saliva saps moisture from them.
A condition called "drug-induced ulcer of the lip" is described as being characterized by painful or tender, well-defined ulcerations of the lip without induration. It is the result of oral administration of drugs, and the condition resolves when the drugs are stopped. Exfoliative cheilitis
Also termed "cheilitis exfoliativa" or "tic de levres", is an uncommon inflammatory condition of the vermilion zone of the lips, which become painful and crusted. There  is continuous production and desquamation (shedding) of thick, brown scales of keratin. The keratin layer of the epidermis of the lips experiences a faster growth and death rate than normal and desquamates. When these scales are removed, a lip of normal appearance is revealed beneath, although  there may be associated erythema and edema. The condition has not yet been attributed to any particular cause. Rarely are infections to blame. In some individuals, there is an association with stress, anxiety, depression or personality disorders. In one report, 87% of individuals had some form of psychiatric disturbance, and 47% had thyroid dysfunction, which in turn can cause psychiatric conditions like depression.Some cases of exfoliative cheilitis are thought to represent factitious damage, termed "factitious cheilitis" or "artifactual cheilitis", and are related to repetitive lip picking or licking habits. This appears as crusting and ulceration caused by repetitive chewing and sucking of the lips. Some consider habitual lip licking or picking to be a form of nervous tic. This habit is sometimes termed perlèche (derived from the French word pourlècher meaning "to lick ones lips").