Brown Fingernails – Causes Of Brownish Color, Spots, Streaks

Many people do not give the fingernails much thought beyond the need to cut, trim and decorate it. However, the fingernails can also be an important indicator of a person’s health. Normally the nails are somewhat white to light brown in color with a pink to red tinge due to the underlying blood flow. There may be some degree of variation in this white color which is considered normal, similar to the variations in teeth color. When the fingernails are overtly discolored then it may be a sign of a nail problem or an underlying systemic disease.

There may be many different colors evident in discolored nails.  A brownish discoloration is one such abnormality which is referred to as melanonychia. It can affect the entire nail or occurs as spots, streaks or bands. Racial variations in skin and nail color may also sometimes be incorrectly described as discoloration but this type of racial melanonychia is considered to be normal. It can also occur during pregnancy but will often resolve after childbirth. These causes are not considered to be serious or a symptom of some underlying disease although it could arise with certain disease in pregnancy.

External Causes of Discoloration

Brown discoloration of the nails can occur due to external factors. There may be no internal abnormality that leads to the change in nail color and if the external factor is removed, the nails should return to a normal color with time. Some of these factors may include:

• Tobacco smoking
• Paint, ink or dye contact
• Excess use of nail polish remover
• Heat damage to the fingers
• Certain nail polish/varnish
• Mechanical trauma to the nails including nail biting
• Radiation exposure
• Sunlight
• Foreign body under the nail

Skin and Nail Diseases

The are a number of skin and nail diseases that may be responsible for the brown discoloration. This includes:

• Nail fungus (onychomycosis)
• Psoriasis
• Lichen planus
• Nevi
• Scleroderma

Onychomycosis

This is a fungal infection of the nail caused by a group of fungi known as dermatophytes. These fungi are also responsible for infections (“ringworm”) of the skin especially on the feet (tinea pedis or athlete’s foot) and groin (tinea cruris or jock itch). Although the feet and groin are the most affected, the hands and fingernails  may also be affected just as skin anywhere on the body.

Picture of onychomycosis of the toenails

Psoriasis

Psoriasis is an autoimmune condition where the body’s immune system targets the skin. It is associated with abnormalities in skin cell turnover and leads to thick plaques of skin, that are usually rough, itchy and silvery white in appearance. Psoriasis may also affect the finger and toe nails.

Deficiency or Toxicity

A yellow, brown to gray discoloration of the fingernails and often the toenails as well may be seen with a deficiency of certain macro- and micronutrients. This includes:

• Vitamin B12 deficiency
• Zinc deficiency (specifically with acrodemaritis enteropathica discussed below)
• Malnutrition

An excessive intake or exposure to certain substances can also cause fingernail discoloration. This includes:

• Arsenic
• Iodine
• Fluoride
• Mercury
• Thallium

Drugs

A number of drugs can cause a brown discoloration of the nails. It is usually not specific to the fingernails unless topical medication is applied to the area. These drugs may include:

• Certain antibiotics like tetracycline
• Some antiretrovirals (ARVs) like lamivudine
• Chemotherapeutic agents
• Corticosteroids
• Gold salts
• Phenythoin
• Psoralens
• Certain tricyclic antidepressants like clomipramine

Genetic Conditions

The two main genetic conditions where brown discoloration of the fingernails may occur are acrodermatitis enteropathica and keratosis follicularis (Darier disease).

Acrodermatitis enteropathica

It is a rare genetic condition that is inherited. In acrodermatitis enteropathica the body’s ability to absorb zinc from the intestine is compromised due to a defect with the genetic coding for the zinc transporter protein (ZIP4). As a result a zinc deficiency occurs.

Keratosis follicularis (Darier Disease)

This is another rare genetic condition. It predominantly affects the skin and is thought to be due to a defect that affects the way calcium is transported into cells. It leads to the cells sticking together in an abnormal way.

Hormone Disorders

A brown discoloration of the fingernails may be seen with a number of endocrine diseases. These are conditions where there is a disturbance in the quantity and/or functioning of certain hormones or the glands that produce it. The nail discoloration may be seen with Addison disease, Cushing syndrome, hyperthyroidism (overactive thyroid) and diabetes mellitus.

Addison Disease

Addison disease is a condition where there is a dysfunction of a part of the adrenal gland that produces two types of hormones – mineralocorticoids and glucocorticoids. As a result there is lower than normal levels of these hormones. Darkening of the skin is a common feature and this may involve the fingernails.

Picture of hyperpigmentation (gums) in Addison disease

Cushing Syndrome

In Cushing syndrome the level of a group of hormones known as glucocorticoids is higher than normal. These hormones are produced by the adrenal gland. The main glucocorticoid is cortisol. While the problem may lie with the adrenal gland, it can also occur from external administration of cortisol (exogenous), in the form of prescription medication.

Cancer

Although rare, a brown discoloration of the nails may be seen with certain types of skin cancers like a malignant melanoma or basal cell carcinoma. The discoloration evident on the fingernails may actually be due to the cancer affecting the nail bed. The correct term for a melanoma occurring under the fingernail is a subungal melanoma. A growing discoloration should always be investigated as soon as possible even if there are no other signs and symptoms indicative of cancer. A brown to gray discoloration of the nails may also be seen in breast cancer although this is uncommon.

 Picture of malignant melanoma

Other Diseases

 There are number of different conditions involving various organs and systems of the body where brown spots, streaks, bands and discoloration of the skin may be seen. This includes:

• Acquired immunodeficiency syndrome (AIDS)
• Cardiovascular diseases like infective endocarditis
• Hemosiderosis
• Hyperbilirubinemia (high bilirubin levels evident as jaundice
• Kidney failure*
• Liver disease*
• Peutz-Jeghers syndrome
• Porphyria
• Systemic lupus erythematosus (SLE)

*A half white and half brown discoloration of the nails is known as Terry’s half and half nails and is seen in certain instances of renal failure and liver disease.

References

1. Melanonychia. Medscape

Last updated on September 8, 2018.