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Ugly toenails are not the exclusive purview of the elderly, but “as you get older, you are more prone to picking up a nail fungus and to having less circulation in your toes, which can affect the way nails grow,” said Dr. Cary Zinkin, a spokesman for the American Podiatric Medical Association.

Toenail fungus is one of the most common causes of ugly nails, and it distorts their shape and makes them thick and ragged or crumbly looking. People with age-related conditions like diabetes and poor circulation are particularly susceptible to nail fungus.

Fungus thrives in dark, moist, warm environments like sweaty enclosed shoes, and “older people often can’t reach their feet to dry them as well as they’d like after a shower, and they put their shoes on without socks,” creating ideal conditions for fungus to take hold, he said.

Older people may also not be able to tolerate the side effects of oral treatments for nail fungus like Lamisil (terbinafine), which can damage the liver, and topical creams may be less effective.

Trauma or an injury, such as dropping a heavy object on your toe, stubbing your toe very hard or getting it caught in a door, can also make for ugly toenails by permanently damaging the nail root and nail bed that the nail grows from, making the toenail grow abnormally. The result can be misshapen, thickened or yellowed nails. Runners and people who wear tight-fitting shoes can also damage their nail beds.

Dr. Zinkin recommends always wearing socks when you wear shoes and changing your shoes often. “Don’t wear the same shoes every day; let your sneakers dry out; and wear socks that are a cotton-fiber mix that can soak up moisture. And wash — and dry — your feet every day.”