The color and overall health of your nails can be a reflection of your overall general health, according to MayoClinic.Com. Healthy toenails and fingernails are free of dents, ridges and abnormal shape or color. Toenails turn yellow for more than just one reason; however, if you notice a pronounced, sudden change in nail color and shape, report it to your doctor, advises the American Academy of Dermatologists, or AAD 3.

About Toenails

A protein called keratin makes up your skin and hair, explains the AAD. Your toenails grow because living cells under your cuticle continue to replicate. As they do, older, dead cells are pushed forward to form hard shells–nails–that protect the tips of your fingers and toes. Your toenails grow more slowly than your fingernails, at a rate of 1 millimeter a month, compared to 2 to 3 millimeters, says the AAD. As you age, the rate at which your nails grow slows, says the National Institutes of Health 4. Aging isn't responsible for all changes in your nails, states the NIH; yellowing may be due to other causes, including infections and medical conditions.

Toenail Fungal Infections

Weak Fingernails

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Yellow toenails are characteristic of a common fungal nail infection called onychomycosis, which affects some 12 percent of the U.S. population, according to the AAD. Dermatrophytes and yeast are the two organisms that are typically responsible for a fungal nail infection. Toenails are more susceptible to fungal infections because they're housed in closed shoes, which provide a warm, dark, moist environment–the perfect conditions for fungi. Toenails darken and become brittle and thick. In some cases, they may actually separate from the nail bed, says the AAD. Fungal nail infections are extremely persistent and difficult to get rid of, even with medical treatment. MayoClinic.Com stresses the importance of seeing a doctor at the first sign of nail fungus 2.

Yellow Nail Syndrome

Yellow nail syndrome is also characterized by a yellowing and thickening of the nails, as well as separation from the nail bed. Most people experience yellow nail syndrome in middle age 1. Even if underlying health conditions are treated, the nails typically remain affected.

Other Causes

How to Get Rid of Thick Skin Under the Toenails

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In some cases, yellow toenails and fingernails have a more innocent cause–wearing darkly-tinted nail polish, such as various shades of red, says skin care expert Paula Begoun. The yellow tinge you see is only a stain and can be remedied by applying a coat or two of base coat before you paint on polish or simply taking a break from nail polish entirely. To remove yellow staining caused by dark polish, Begoun suggests first buffing the top of the nail and soaking in 3 percent hydrogen peroxide for a few minutes.

Self-Care

Keep toenails healthy by regularly clipping them short. Cut straight across with manicure scissors or clippers. If it's difficult to cut thickened toenails, the AAD advises soaking your feet in warm salt water for up to 10 minutes, then rubbing a cream that contains lactic acid or urea into the nails. Make sure your shoes fit appropriately, and alternate footwear daily to give sweat-dampened shoes time to dry out.