Why thighs chafe and what helps when you run
Short answer: Thighs chafe because skin rubs against skin or fabric, especially when it is warm and damp. Longer legs on your underpants can help, because the fabric sits in between. Here you can see what is behind it and what you can do yourself.
Why chafing happens on the thighs
Chafing happens when skin repeats the same movement against something that rubs. When you run, your thighs do it thousands of times. Heat and sweat make it worse, because the skin gets more sensitive and friction goes up. That is why many only notice it on longer runs or on warm days.
Longer legs between the thighs
Longer legs on your underpants put a layer of fabric between the two skin surfaces and cut down friction. Look at bamboo underpants for men, where you can compare leg lengths. Make sure the legs do not ride up, because then it will not work, and the leg edge can become a new source of rubbing.
The fit should be close, not tight
Underpants with long legs should sit close enough that they do not shift, but not so tightly that the edge cuts in. If they shift, they rub themselves, which defeats the purpose. Try them on a short run or a brisk walk before you take them on a long distance.
Underpants with long legs for running
Many runners choose underpants with long legs, because they can make a difference on long distances. Pick a length that covers the area where the thighs meet. If you need an extra layer under your shirt, a bamboo undershirt for men can help when you get warm and the skin turns damp.
The fabric and the sweat
Bamboo in clothing is viscose made from bamboo, and many find the fabric soft and easy to wear. Moisture raises friction with any fabric though, so change into dry clothes after your run. Wash the clothes by the care label so they are ready for the next run without rubbing the skin.
Small habits that help
Keep the skin clean and dry, and change clothes when you finish running. Do not wear clothes that are wet with sweat for longer than necessary. You can also try shorter runs while your body adjusts, and see whether the rubbing eases. Small things can make a difference.
When the skin is already irritated
If the skin is red or sore, give it a break from whatever rubs, and keep it clean and dry. If it does not go away or gets worse, talk to your doctor. Clothing cannot do everything here, and you should not simply keep running if it hurts.
Combine with the rest of your clothes
Rubbing does not only come from the underpants. A shirt, shorts and seams can chafe too, so choose clothes that fit evenly. By using similar fabrics, such as bamboo T-shirts for men, you get a more even feel on the skin and fewer spots that can rub while you move.
Frequently asked questions
Does it help to run in long underpants?
Many find that longer legs help, because the fabric cuts down friction between the thighs. It is personal though, so try a short run first and notice whether the legs stay in place.
What do I do if my thighs already chafe?
Give the skin a break, keep it clean and dry, and avoid whatever rubs. If it does not go away, or the skin is very sore, talk to your doctor.
Do the underpants need to be tight to help?
No, they should sit close enough not to shift, but not so tight that the edge presses. A suitably close leg that stays in place works best.
