If a toenail is allowed to grow too long, it can jam the end of the shoe, causing a microtrauma with each step, Napolitano said. Thousands of such microtraumas can discolor the toenail.

Repeated microtraumas also can lift the toenail off the nail bed. This can cause a blister to form under the toenail. It also can make the toenail more prone to fungal infections, which can lead to discoloration, thickening, brittleness and even loss of the toenail.

'By following a few simple guidelines, you can keep your toenails healthy while also looking great in sandals,” Napolitano said.

Napolitano offers these toenail tips:

• The toenail should extend no farther than the end of the toe. So when cutting your toenail, leave only a sliver of white at the end of the nail. The toenail should be even shorter if you do high-impact activities such as running and Zumba classes.

• If you polish your toenails, use a base coat. Painting your toenails red without a base coat can discolor the toenail.

• It’s easier to cut your toenails after a shower, when the nails are softer.

• After cutting your toenails, use an emery board to file away any sharp edges. File in one direction only – not back and forth.

• Common toenail clippers, available at pharmacies, are inexpensive. But they can leave jagged edges, or cut too deeply. Nail nippers, which look somewhat like pliers and are available at beauty supply stories, cut with greater precision. But they also are more expensive.

If you go to a nail salon, Napolitano offers these further tips:

• Make sure the salon is clean. As a rule of thumb, if you would not feel comfortable walking around the salon barefoot, go somewhere else.

• Ask how the salon cleans its instruments. The best method is autoclave, which sterilizes with high-pressure steam. Also acceptable is sterilizing equipment in a solution. With either method, equipment must be sterilized after each use.

• If you have open sores, do not use the whirlpool footbath.

• Let the salon know if you are a diabetic or are taking a blood thinner.