The naturally pink color of the inside of the mouth and lips is due to the thin lining over these areas. It allows the redness of blood to show through to some degree masked partly by the melanin (natural pigment) in the overlying areas, like on the skin of the lips. However, sometimes there may be darkening in the inside of the mouth and of the lips which could be due to various medical conditions.
What is Oral Hyperpigmentation?
Oral hyperpigmentation refers to darkening of the inside of the mouth. This term may also extend to the lips (labia oris). Sometimes darkening of the mouth may occur on its own as is the case with darkening of the lips, while at other times the darkening in both these areas may occur simultaneously. It can vary in intensity and even in color to some degree.
Darkening of the body surfaces, also known as hyperpigmentation, is usually due to the overproduction of melanin. This natural skin pigment is present in skin to varying degrees which is influenced largely by genetic factors hence the racial/ethnic differences in skin color. It is also influenced by trauma, be it through sunlight overexposure or injury to the skin.
Sometimes hormonal factors, chemicals and even drugs can alter the natural pigmentation and lead to darkening. It is important to understand that hyperpigmentation is usually not a condition on its own but a sign of some underlying medical problem.
Reasons for Oral Pigmentation
The inner lining of the mouth is a thin mucous membrane and not skin. Since is so thin the underlying blood flow in tissue is therefore visible as a pinkish hue. This extends from the inner cheek to the roof of the mouth and tongue and is continuous with the nose and throat lining. It also continues to the inner part of the lip.
However, the lip surface is covered by skin that is thinner than skin elsewhere on the body. Therefore the underlying tissue and pink hue is more visible on the lips than the surrounding skin. Unlike the inner mouth, the lips is constantly exposed to bombardment from the environment including climatic changes.
Darkening is a consequence of the deposition of substances, some of which are natural pigments. The pigments that cause darkening may originate internally within the body or externally from substances that are ingested or inhaled. These endogenous or exogenous substances may either directly cause darkening of the skin and mucous membranes, stimulate darkening or react with other substances to give rise to pigmentation.
Causes of Dark Mouth and Dark Lips
There are a number of different causes of darkening within the mouth and on the lips. Some may be due to dietary and lifestyle factors while other causes may be linked to poisoning and various diseases.
Dye in Edibles
Foods, beverages and treats may have strong dyes that can color the lips and oral cavity a darker color. This is often seen with certain candies and gums. Sometimes these dyes are not easily visible in the edible and only noticed after eating. Children may also chew on the graphite in pencils and colored markers which can also taint the lips and mouth, albeit temporarily.
Tobacco chewing may also cause darkening in the mouth. This can arise from the tobacco pigments but there are other reasons why it may also occur. For example, smoker’s melanosis which may be seen in tobacco smoking is a result of irritation of the lining as a result of the smoker.
Areca nut chewing is a common practice in certain South Asian countries like India. The nut is crushed, mixed with other substances like tobacco and then wrapped in a lead. It causes redness of the lips and mouth but over time this can lead to darkening.
Both mechanical and chemical injury of the lips and inner lining of the mouth can also cause hyperpigmentation. This can vary from chipped teeth and poorly fitting dentures that cause constant trauma, to lip biting and the use of certain chemicals in mouth washes like chlorhexidine.
Lip cosmetics cause darkening for various reasons. It may not occur with all cosmetics but if the ingredients within makeup like lipstick contain heavy metals such as lead or irritate the skin then darkening may gradually develop.
The lips in particular may take on a pale to grey appearance when it is excessively dry. This drying can occur due to environmental factors such as wind, heat and cold. However, dehydration is another cause as is seen in conditions where there is severe fluid loss such as profuse diarrhea.
Iatrogenic hyperpigmentation refers to darkening caused by medication or other substances and devices used for medical purposes. Certain antibiotics and antimalarial drugs may sometimes cause this type of darkening as can chips of amalgam fillings.
The ingestion of certain metals may also lead to darkening in various areas of the body. This includes metals such as bismuth, lead, mercury and silver. It can range from blue to grey and even black discoloration within the mouth or of the lips.
Cyanosis is the medical term for a bluish discoloration that arises with inadequate oxygen levels in the blood. This can occur for various reasons including severe anemia, heart failure, respiratory disorders and with asphyxiation.
The accumulation of bilirubin in the body and its subsequent deposition in tissue such as the ‘whites’ of the eyes, inner lining of the mouth and skin is known as jaundice. It results in a yellowish discoloration but depending on other factors it may contribute to darkening.
Since the lip has skin on it, various skin diseases could occur on the lips and lead to darkening. One of the more common of these conditions is contact dermatitis which could be linked to irritants or allergens that touch the lip surface.
A host of diseases may cause darkening in the mouth and of the lips for different reasons. This includes:
- Addison’s disease
- Anemia (severe)
- HIV-associated melanosis
- Kaposi sarcoma, a type of cancer seen with HIV/AIDS.
- Oral melanotic macule
- Peutz-Jeghers syndrome
- Pituitary gland disorders