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Sudden changes to the shape and color of toenails can be unsettling. Yellowing can affect the entire nail or show up in discolored patches, making the toes look opaque and sickly.

Yellow toenails are a relatively common issue with many potential causes. Additional circumstances and symptoms can help people discover the cause of their discolored nails and how to treat them.

Fungal Infections

Feet provide a warm, damp environment that is perfect for microscopic fungus. When fungus makes its home underneath a toenail, it's called onychomycosis. The organisms feed off nail tissue, irritating the skin and causing the nail to thicken and change color. Sometimes this is itchy or painful.

Fungal infections are notoriously tricky to treat, but a combination of antifungal creams and keeping the affected toe clean and dry can help.

Woman applying ointment to foot PhotoAlto/Odilon Dimier / Getty Images

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Onycholysis

Onycholysis is not the same thing as onychomycosis, though it can also be caused by a fungal infection. The former is a condition where the hard part of the nail or nail plate raises off the nail bed. The underside is then exposed to oxygen, which causes discoloration.

Treatment depends on what made the nail lift in the first place. Injury, infection, and even certain medications can cause onycholysis.

A close-up of a foot with a fungus on the nails is examined by a doctor in gloves Irina Tiumentseva / Getty Images

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Cosmetics

Not all yellowed nails are a sign of illness. Nail polish, especially darker shades, acetone nail polish remover, and self-tanners can all leave stains.

These chemical stains are harmless and go away on their own, but a nail bath in three parts water and one part hydrogen peroxide could speed up their removal. Beauty fans hoping to avoid nail discoloration should use a base coat for their toenail polish and stick to lighter shades.

pedicure Wuka / Getty Images

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Bruising

Multiple factors can cause trauma to the nail bed. Wearing shoes that are too tight, not trimming nails properly before high-pressure activities like hiking, and dropping something on the toe can all cause damage.

After these injuries, bruises can form on the nail bed. The nail may turn yellow, black, or purple. See a doctor if the toe is painful, but the bruising should resolve itself over time.

man with black toenail Aitor Diago / Getty Images

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Psoriasis

Psoriasis is a chronic condition that causes scaly, irritated patches of skin. It can tighten the skin around the nail or affect the nail bed itself, causing thicker nails, pitting, and yellowing.

There is currently no cure for psoriasis, but steroid injections, skin creams, and medication may help relieve symptoms. A dermatologist can recommend the best course of treatment.

A toe with nail psoriasis. Imagesines / Getty Images

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Yellow Nail Syndrome

Yellow nail syndrome is a rare disorder that affects the lymphatic system. Curved, thick, yellow-tinted nails that stop growing and may even fall out are the most visible symptoms. The nails remain relatively clear and smooth, which helps distinguish yellow nail syndrome from other conditions like psoriasis.

This condition can also cause chronic bronchitis, coughing, shortness of breath, and swelling under the skin. Treatment is tailored to the symptoms and may include antibiotics, vitamin E supplements, and corticosteroids.

yellow toenails LENblR / Getty Images

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Thyroid Diseases

Both hyperthyroidism (where the thyroid gland produces too much hormone) and hypothyroidism (where the thyroid gland produces too little) can cause yellow toenails.

Nails affected by a thyroid disorder might be brittle and prone to crumbling. They tend to grow slowly or not at all. Symptoms should ease with hormone replacement therapy.

Close-up of male toes with a cracked nail inside-studio / Getty Images

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Diabetes

Foot problems are common with diabetes, especially uncontrolled diabetes, because of damage to the circulatory and nervous system in the legs. Circulatory issues could make nails brittle, thick, yellow, and opaque. The toenails are also more vulnerable to infection and injury.

Glucose control via diet, exercise, or insulin injections helps to prevent diabetic flare-ups, but people with diabetes still need to monitor their feet for emerging issues.

A podiatrist examines a sore foot with destroyed nails

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Jaundice

Jaundice tends to be easily recognizable because it affects the skin and the whites of the eyes as well as the nails.

Liver disease, hepatitis, infection, gallstones, and tumors can cause jaundice, and it is also a side effect of some medications. Sometimes, it's caused by a temporary imbalance of bilirubin in the blood, which goes away on its own. Treating the underlying condition usually helps.

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Old Age

In some people, yellow nails are just a part of getting older. Toenails in particular become thicker, more brittle, and more prone to becoming ingrown in old age. Sometimes grooves appear on the surface of the toenail, running lengthwise down the nail bed.

It's still worth seeing a doctor to make sure that there isn't another issue, especially if a person experiences other symptoms. In the absence of other causes, however, yellow nails in older people may be perfectly normal.

Feet of old woman Rosmarie Wirz / Getty Images

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Disclaimer

This site offers information designed for educational purposes only. You should not rely on any information on this site as a substitute for professional medical advice, diagnosis, treatment, or as a substitute for, professional counseling care, advice, diagnosis, or treatment. If you have any concerns or questions about your health, you should always consult with a physician or other healthcare professional.