Quick summary
- Cause: repeated friction, made worse by sweat, salt, heat, rain and seams.
- Prevent: anti-chafe balm before every long run, fitted moisture-wicking kit, and no cotton.
- Hot spots: inner thighs, underarms, nipples, sports-bra line, waistband and feet.
- Test: anything that rubs slightly at 15 km will rub badly at 30 km. Fix it in training.
- Treat: clean gently, keep the area dry and protected, and let it heal before your next long run.
Chafing is one of the most common problems runners face on long runs, and one of the most avoidable. It usually starts as a slight sting and ends as raw, painful skin that can make the last 10 km of a race miserable and the shower afterwards worse. Almost all of it can be prevented with the right kit and a few minutes of preparation.
What causes chafing
Chafing happens when skin rubs repeatedly against skin or fabric. Four things make it worse:
- Moisture: sweat and rain soften the skin and increase friction.
- Salt: dried sweat leaves salt crystals that act like sandpaper.
- Duration: the longer you run, the more repetitions of the same rub.
- Loose or heavy fabric: baggy or wet fabric moves more against the skin, and cotton holds water.
That's why chafing often appears only on long runs, in hot or humid weather, or in the rain.
Prevention: the basics
- Use an anti-chafe balm or stick on every hot spot before runs longer than about an hour. Reapply on very long runs or in rain.
- Wear fitted, moisture-wicking fabric. Synthetic technical fabrics and merino dry faster and move less against the skin than cotton.
- Choose kit with few seams in high-friction areas, and flat seams where they can't be avoided.
- Make sure kit fits now, not how it fitted last year. Waistbands and bra straps that are too tight or too loose both cause rubbing.
- Test everything on long runs of 15 km or more before using it on race day.
A fix for every hot spot
| Hot spot | Common cause | Fix |
|---|---|---|
| Inner thighs | Skin-on-skin rubbing, especially in heat | Anti-chafe balm; fitted half tights or shorts with a built-in liner |
| Underarms | Arm swing against seams or fabric | Balm; singlets with low armholes and no seams under the arm |
| Nipples | Shirt fabric rubbing, common in men over long distances | Plasters or nipple guards before the run; smooth, fitted tops |
| Sports-bra line | Band or strap rubbing under load | Balm along the band and straps; a well-fitted bra with soft, flat seams |
| Waistband and lower back | Shorts or a belt bouncing | Snug waistband; a running belt that doesn't bounce; balm along the line |
| Neck and collar | Collar seam rubbing, especially with a hydration vest | Collarless or low-neck top; balm on the neck |
| Feet and toes | Friction in shoes, damp socks | Synthetic or merino socks; shoes that fit with a thumb's width at the toe; balm between toes |
For blister-specific tips and a full race-day list, see our marathon kit checklist.
Running in heat and rain
In heat, you sweat more and salt builds up faster. Apply balm generously, consider rinsing salt off at aid stations or water stops, and choose the lightest, most breathable kit you have. Our guide to running in hot weather covers kit and hydration.
In rain, wet fabric gets heavier and clings to the skin. Choose fitted rather than loose kit, use more balm, and avoid heavy cotton layers entirely.
How to treat chafed skin
If you do chafe:
- Clean the area gently with lukewarm water and a mild, unperfumed soap. The first shower will sting; this is normal.
- Pat dry. Don't rub.
- Protect it with a thin layer of a gentle barrier ointment, such as petroleum jelly, and loose clothing.
- Let it heal before your next long run, usually a few days for mild chafing. Cover healing skin and use extra balm when you return.
See a doctor or pharmacist if the skin shows signs of infection, such as increasing redness, warmth, swelling, pus or fever, or if it doesn't heal within a week or two.
Race-day anti-chafe routine
- Apply balm to every hot spot after dressing, 30–60 minutes before the start.
- Plasters or nipple guards on, if you use them.
- Carry a small stick of balm in a pocket for long races, or use the petroleum jelly many races offer at aid stations.
- Wear only kit you've tested on runs of 25 km or more.
FAQ
What is the best way to stop thigh chafing when running?
Apply anti-chafe balm to the inner thighs before every long run and wear fitted half tights or shorts with a liner that covers the area where your thighs touch. Test the combination on a long run before race day.
Why do I only chafe on long runs?
Chafing builds with repetition, sweat and salt. Short runs don't create enough friction or salt build-up to break the skin, but after 60–90 minutes the same rubbing becomes enough to cause damage.
Does petroleum jelly work for running chafing?
Yes, petroleum jelly reduces friction and is widely used. Dedicated anti-chafe balms and sticks are less greasy and easier to apply, and some last longer in sweat and rain.
How do I stop nipple chafing when running?
Cover the nipples with plasters or purpose-made nipple guards before long runs, and wear a smooth, fitted, moisture-wicking top. Loose cotton tops are the most common cause.
How long does chafing take to heal?
Mild chafing usually heals in a few days if kept clean, dry and protected. Deeper or broken skin can take longer. See a doctor or pharmacist if it shows signs of infection.
This article is general information, not medical advice. If chafed skin becomes infected or doesn't heal, see a doctor or pharmacist.