Everything You Need to Know About Blisters

Here’s what to do if you get a blister and how to prevent it from affecting your running again.

To put it simply: dealing with blisters is an actual pain. If you’re here, you probably already know that blisters are those red, raised areas that look like bubbles and occur mostly on the feet. Located on the upper layer of skin, they often fill with fluid and may also hurt or itch.

Many runners incur them during races, especially marathons, due to an increased friction between your skin and sock or shoe. But blisters can pop up at any time, including during training runs, and be caused by non-running footwear.

While most blisters don’t pose a serious health risk, they shouldn’t be taken lightly. A painful blister can sideline a runner – or worse – get infected especially if you use an unsanitary needle to pop it.

Common Causes of Blisters

Annoying and painful, blisters are caused by friction. For runners, the culprits are usually your socks, shoes, or both rubbing against your skin. Anything that intensifies rubbing can start a blister, including a faster pace, poor-fitting shoes, and foot abnormalities, such as bunions, heel spurs, and hammertoes. Heat and moisture intensify friction by causing your feet to swell.

Blisters commonly pop up during races or long runs when mileage is increased and friction occurs without intervention. Your body responds to this friction by producing fluid, which builds up beneath the skin that’s being rubbed.

And since moisture is also a factor, races are the perfect breeding ground for blisters: you’re perspiring more by running faster and longer, sloshing through water stations and, if the weather is warm, possibly pouring water over your head.

Blister Treatment

If you have a large blister that’s big, nasty, even purple, and it’s affecting how your toes bend, give it a day or two to shrink, says Dr Jordan Metzl, a sports medicine physician and host of Runner’s World’s IronStrength workout. If it doesn’t go down, see your doctor to have it popped in the office under sterile conditions so it doesn’t get infected.

If you have a small blister that’s not prohibiting your movement, leave it alone. “When the skin and the membrane of the skin are compromised by popping the blister, all of the bacteria that live on the skin normally can invade and could cause inflammation or an infection right away,” Metzl says. You could end up making a very small problem much bigger by puncturing the barrier. You should also leave small blood blisters intact too. Otherwise, you risk getting bacteria in your bloodstream. Cover it up so it goes down, then try to fix the problem that caused it (see prevention methods below).

To treat small blisters, cut a hole the size of the blister in the middle of a piece of moleskin like Dr. Scholl’s Moleskin Roll (amazon.com) then place it over the blister and cover with gauze. The blister will dry out and heal on its own. Or try covering the blister with a waterproof pad like Band-Aid Blister Gel Guard  (amazon.com) or KT Tape Performance+ Blister Treatment Patch  (amazon.com).

If you absolutely must pop a blister (for example, if you’re travelling and can’t see your doctor), use caution. Metzl suggests cleaning the area and needle with soap and water and following with an antibiotic ointment. Then be sure to clean the area regularly to prevent infection.

A blister under a nail is best treated by a professional. You never want to deliberately remove the toenail.

Blister Prevention

To stop blisters before they even start to form, Metzl recommends making sure you’re wearing running shoes in the right size. Shoes that are too small will cause blisters under the toenails or on the tops or tips of the toes. There should be a thumb’s width of space between the toes and the end of the toe box. Your socks should fit smoothly with no extra fabric at the toes or heels. If you suspect yours don’t fit, head to your local running store to have an associate help you find your size. Or look for socks with reinforced heels and toes to help reduce friction.

Metzl also recommends using products that dry out your skin such as baby or anti-chafing powders or using a lubricant or anti-chafing balm on risky areas.


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