Why do I get black toenails?

That black color is usually a blood blister under the nail. The most common cause is your toe hitting the front of your shoe over and over.

Downhill running aggrevates it, because your foot slides forward with every step. Hot weather makes it worse, because feet swell in the heat. Cold weather can too, if the extra sock you added made the shoe too tight.

Over several weeks the nail will usually loosen and fall off, and a new one grows in behind it. Don't pull it off yourself. A podiatrist can take it off cleanly if it needs to come off.

If the pressure is genuinely painful, there is a procedure to drain the blood and relieve it. Do not attempt this at home with a heated paperclip or a drill, which is exactly what people try. Go see somebody. It takes a few minutes in an office and you leave feeling better.

Preventing It

Start with the shoes. Running shoes usually need to be a half size larger than your street shoes so your toes have room in the front. If there's a running store near you, get properly fitted. You may need different sizes for different seasons.

Keep your toenails trimmed short and straight across so they aren't pressing into the shoe.

And learn to lace for downhill running. The heel lock, where you use the extra eyelet at the top to cinch your heel back, keeps your foot from sliding forward without having to crank the whole shoe tight.

One thing to watch for.

Not every dark nail is a bruise. If discoloration shows up without you banging your toe on anything, or if a dark streak stays put and doesn't grow out over a few months, get it looked at. Fungal infections and, rarely, a form of skin cancer can look the same as a runner's bruise.

Can I run during my period?

Yes. The idea that women shouldn't is a myth. Unless something is seriously wrong, in which case see a doctor, running usually helps.

Movement tends to ease cramps, likely through a combination of endorphins and increased circulation to the area. It reliably improves mood, which is worth something on its own.

If you're training for a race, deliberately schedule a run during your period. A couple of practice runs mean race day won't be the first time you've dealt with it.

For gear, you have more options than you used to. Tampons, menstrual cups, discs and period underwear all work for running, and cups are popular with distance runners because they hold more and don't need changing mid-run. Most runners find pads chafe. Try things on training runs, not race day, and carry a spare on long runs.

Two things worth knowing.

Heavy periods are a common cause of low iron, and low iron feels exactly like bad training. Everything is harder, you're winded sooner, and you're tired in a way rest doesn't fix. If that's you, ask your doctor for a ferritin test.

And if your period stops, that isn't a sign you've gotten fit. It's a signal worth taking to a doctor.

The general rule is to pay attention. Drink enough, and take a day off if you need one.

Does running cause acne?

Not the running, it's usually the rubbing.

Anything tight or repeatedly rubbing against skin can cause a form of acne called acne mechanica. The usual spots are under watch bands, bra straps, belts, headbands and heart rate monitor straps.

Loose or moisture-wicking clothing helps, and so does getting out of wet gear as soon as you're done.

Sweat mixed with makeup and sunscreen can also clog pores, especially if it sits on your skin for an hour after you finish. Shower as soon as you can.

You don't need makeup to exercise. If you wear it anyway, look for non-comedogenic on the label.

Sunscreen is different, and living here I'm not going to tell you to use less of it. Wear it. If it's breaking you out, switch to a mineral formula with zinc oxide or titanium dioxide, or something labeled non-comedogenic, and wash it off once you're out of the sun.

For anything more stubborn, a body wash made for acne is a reasonable start, and a dermatologist can walk you through benzoyl peroxide and retinoids. One warning nobody gives you in advance: benzoyl peroxide bleaches fabric. It will take the color out of your towels, your pillowcase and your favorite running shirt. Use white ones.

None of these are reasons to stop running. They're reasons to fix your shoes, plan ahead and shower faster.

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12/16/2017
Updated 8/30/2026