Natural Color of Lips
The human lips (labia oris) is the junction between the outer facial skin and inner buccal mucosa that lines the mouth cavity. The outer layers are largely similar to skin except that the lips has fewer layers. The color of skin is determined by the amount of natural pigment known as melanin. Melanocytes are specialized pigment cells that produce melanin in smaller quantities than elsewhere on the skin. The lips also have melanin but to a much lesser degree than the rest of the skin.
This lower quantity of melanin is genetically determined but is further regulated by exposure to ultraviolet light mainly from sunlight and less frequently from tanning beds. Combined with its fewer layers of skin than the rest of the face, the color of the lips is also largely dependent on the underlying tissue color and blood flow. This is the reason that the lips are a pink to red color.
Discoloration of the Lips
Most cases of discolored lips are associated with brownish to brownish-gray hue. The lips itself almost never reaches a full black color. However, other colors such as bluish or yellowish discoloration may also occur. It can be associated with environmental causes, mechanical, chemical or electromagnetic damage, skin disorders, systemic diseases and lifestyle factors.
Causes of Dark Lips
Anemia is one of the common causes of lip discoloration particularly in women during the reproductive years. It is often related to iron-deficiency anemia but any type of anemia can be responsible. Anemia is a lower than normal concentration of the oxygen-carrying compound known as hemoglobin. This may be due to fewer red blood cells or less hemoglobin within these red blood cells. Hemoglobin is responsible for the naturally red color of blood. Since the lip color is partly imparted by the blood flowing through the lips, a deficiency of hemoglobin or red blood cells will affect the lip color accordingly. In severe cases this discoloration may be slightly blue and becomes more pronounced with cold weather.
Cyanosis is a bluish discoloration of certain parts of the body associated with a higher than normal level of deoxygenated blood. This can be caused by any number of blood, cardiovascular and pulmonary diseases as discussed under causes of cyanosis. The bluish tinge may become worse or only become apparent with exercise or in cold weather. Cyanosis is a serious condition that needs to be investigated further and the cause treated appropriately. Emergency medical attention is necessary if blue lips are associated with a diminished level of consciousness, cold and clammy skin and difficulty breathing.
Cigarette smoking, alcohol abuse and regular narcotic use may all cause discoloration of the lips. Cigarette smokers may have darkening of the lips and inner lining of the mouth known as smoker’s melanosis. This only occurs in long term cigarette smoking and will resolve once smoking is discontinued. Certain types of illicit alcohol and home brews may use acidic substances to speed up fermentation which can lead to a dark spots on the lips. Illicit substances that are smoked are more likely to contribute to dark lips. It is one of several distinguishing features of crack cocaine and crystal meth users. Betel leaf and areca nut chewing as well as tobacco chewing may cause an intense redness of the lips but over years this can also lead to a dark discoloration of the lips.
Lentigo is a flat brown to black spot (several spots ~plural : lentigines) that can affect the skin and lips. It may be associated with long term sun exposure (solar lentigines, also known as actinic lentigines or liver spots) or with systemic diseases (non-solar lentigines) like Peutz-Jeghers syndrome.
Peutz-Jeghers syndrome is a genetic condition characterized by the presence of gastrointestinal polyps (read more on intestinal polyposis syndromes) and hyperpigmentation of the skin and mucosal membranes. This condition is associated with a very high risk of intestinal cancer. The darkened skin patches (lentigines) is in most cases accompanied by darkening of the mucosal lining in the mouth (buccal mucosa).
Melasma is hyperpigmentation of the skin associated with increased melanin deposition. It occurs on any surface of the skin that is exposed to sun but on the face in particular. While it has a predilection for the forehead and cheeks, it may also occur on the lips, particularly the upper lip. It tends to form symmetrical patches with no itching or other symptoms of a rash.
Dermatitis is a broad term that refers to skin inflammation due to any number of causes. The two more common causes is contact dermatitis and atopic dermatitis both of which have an immune-mediated hypersensitivity (allergy) component to it. Although atopic dermatitis is uncommon on the lips, sometimes skin lesions on the face close to the lip may extend onto the lip surface. The more likely dermatitis is contact dermatitis particularly in women and with the use of cosmetics such as lip gloss, lipstick and lip liners. These cosmetics may cause a darkening of the lips over time even without the presence of any dermatitis symptoms like itching. It is more likely to be seen with cheaper cosmetics that have certain dyes which are not recommended for use on human skin. The stringent regulations for cosmetic manufacturers means that most reputable brands are unlikely to use these types of dyes.
Jaundice is a yellow discoloration of the skin caused by an excess of bilirubin associated with liver or biliary disease. The yellowing is most prominent on the skin and whites of the eyes (sclera) but may also stain the inside of the mouth (buccal lining). Other causes of yellowish discoloration may include hypocarotenemia which is associated with excess beta carotene derived from foods, pernicious anemia, Wilson’s disease and other causes of copper toxicity. The yellowing is not as prominent on the lips as it is on the other parts of the skin and sclera.
Skin health is largely dependent on adequate moisture and the lips with its fewer layers of skin easily loses its natural moisture. This is more common in cigarette smokers and mouth breathers as the movement of air in and out of the mouth expedites moisture loss. Dry lips can eventually crack (chapped lips) and if it persists it can contribute to slight discoloration of the lips. This is also more likely to occur in cold climates and windy weather. Dry lips appear white or pale with cracking but in severe cases this can extend to the skin around the lips causing a darker brown outer border.
Chronic sun exposure can also cause slight darkening of the lips apart from solar lentigines and melasma mentioned above which present with dark spots or patches respectively. UV light has the same effect of stimulating melanin production as it does on skin on other parts of the body. However, the skin on the lips with its lower melanin content may not be affected as significantly.
Several different types of medication may cause hyperpigmentation and other forms of discoloration of the skin which may affect the lips as well to some extent. This includes :
- Tetracyclines like minocycline which are broad spectrum antibiotics and other types of antibiotics may also be responsible for lip discoloration.
- Chemotherapy drugs used in the treatment of cancer.
- Antimalarial drugs used in the prevention or treatment of malaria.
- Tricyclic antidepressants like imipramine and desipramine.
- Antipsychotic drugs used in the treatment of certain psychiatric conditions. Some drugs like phenothiazines may also be used for treating nausea and vomiting.
- Skin-lightening agents like hydroquinone.
- Certain photosensitizing drugs like isotretinoin and acitretin which are used for the treatment of other skin disorders.
Discoloration of the skin and lips may be associated with eating disorders such as anorexia nervosa and bulimia due to nutritional deficiencies. In terms of bulimia, repetitive vomiting and the corrosive action of stomach acid may inflict ongoing damage on the lips and possibly lead to discoloration over the long term.
Toxins and Poisoning
A number of toxins may cause discoloration of the skin and possibly the lips, particularly metals such as copper, bismuth, mercury and silver. Certain caustic substances such as acids, strong alkalis and other toxic compounds may cause chemical burns on the lips thereby leading to discoloration.