Chafing is skin rubbed sore by friction, and damp skin chafes first because wet skin grips harder. Before you move, a thin layer of tallow balm or petroleum jelly lets skin slide where it rubs, and clothes that wick sweat keep it drier. When it hurts or turns red, it's time to stop.
For that layer, I reach for Bare Silk ($34), the Unscented original, with no essential oils or fragrance. I'd keep scent off rubbed skin. Honey Glow ($42) is our jar for legs that run dry between workouts, and both prices are as of October 5, 2026.
What is chafing, and why does sweat make it worse?
Mailler and Adams, reviewing marathon-day skin injuries in 2004, describe chafing as a surface inflammation where skin rubs under moisture and friction. Heat and damp let the friction split the skin's outermost layer from the one below. What's left is an inflamed patch that can ooze. Across the marathon studies they gathered for the British Journal of Sports Medicine, 0.4% to 16% of runners at the medical tents reported it.
Sweat is why damp spots go first. Derler and Gerhardt reviewed skin friction measurements for Tribology Letters in 2012 and found hydration was the main cause of the variation. Dry skin's friction coefficient was typically around 0.5. Moist or wet skin typically ran above 1, more than double, so the same stride grabs harder once you're sweating.
That's why the inner thighs and underarms are the usual trouble spots. Kalra and colleagues, in a 2014 American Family Physician review, trace the skin-fold rash intertrigo to the same pair: friction and trapped moisture.
What goes on before you move?
Clothes come first, because they decide how wet your skin gets. The American Academy of Dermatology (AAD) recommends moisture-wicking, loose-fitting clothes during physical activity, and no cotton. Cotton soaks up sweat, which can lead to friction and chafing. Mailler and Adams ask for dry, well-fitting clothes, and I read the two together as clothes that don't bind and don't flap. If a seam sits where you already rub, that's worth a different pair.
Then the layer. The AAD says powder or petroleum jelly on problem areas reduces friction where skin rubs skin or clothing. Mailler and Adams call the jelly effective. A tallow balm is a fat, and it does the same slip job. I haven't found a study testing tallow against petroleum jelly for chafing, and we haven't run one.
Thin is the point. Warm a pea of balm between two fingertips and press it onto each spot that rubs before you dress. It doesn't dry sweat. On a humid day the clothes carry more of the load, and a balm does nothing for skin that's already open.
What about runner's nipple?
Runner's nipple, which the papers call jogger's nipple, is the same friction with a shirt doing the rubbing. Mailler and Adams say it's common in distance runners, especially women who run without a bra and men in shirts of coarse fiber such as cotton. Repeated rubbing can leave the nipple and areola red and crusted. Across the marathon studies they reviewed, 2% to 16.3% of runners reported it on race day.
Their answer goes on before long runs: a slick layer such as petroleum jelly, or a cover such as a commercial patch or adhesive tape. They point women toward bras of silk or another soft fiber, and men toward a synthetic shirt that wicks moisture. A thin layer of balm can stand in for the jelly. Crusted or bleeding skin is another matter, and the balm stays off it until it's closed.
When do you stop?
The AAD's rule is plain: stop your activity right away if you feel pain or discomfort, or if your skin turns red. Push on, and that's how a red patch becomes an open one.
Raw or weeping skin is wound care, and the balm stays in the jar, ours included, until it's closed again. That's your doctor's call, or a board-certified dermatologist's. Kalra and colleagues add that friction and inflammation can break skin down and let fungal or bacterial infections in. The AAD's signs for a visit are pus, or pain or swelling that grows. If a rubbed spot isn't calmer within a few days, I'd stop guessing and book the visit myself. It's cosmetic care, not a treatment, and your provider's plan comes first.
What goes on red, intact skin?
Keep the evening plain: a rinse with cool water and a mild cleanser, then a pat until it's just damp. After that, a thin layer of Bare Silk Unscented keeps it from drying tight. Sethi and colleagues, in a 2016 review of moisturizers, describe that kind of layer as an occlusive, a water-repelling film that slows water loss. It works best on slightly damp skin. Skip the layer in deep folds: Kalra and colleagues say a fold kept dry and open to air is less likely to flare again.
So Bare Silk Unscented is the jar I'd hand you. It goes on before you move and on intact skin after, and Honey Glow covers dry legs on the days between.
The jar for this job is Bare Silk ($34). Subscribe to two jars and a third rides free, and every subscription takes 25% off the first delivery.
Questions we hear
Can you put tallow on chafed skin?
Only on intact skin. Red skin that hasn't opened can take a thin layer of unscented balm once it's rinsed and patted until just damp. Raw or weeping skin is wound care. Keep every balm off it, ours too, while your doctor or a board-certified dermatologist takes a look.
How do I stop my inner thighs from chafing?
Start with what you wear: the American Academy of Dermatology suggests moisture-wicking, loose-fitting clothes for exercise and no cotton, which soaks up sweat. It names powder or petroleum jelly to reduce friction, plus moleskin or a soft bandage on the thighs. A thin layer of tallow balm does the same slip job. If it hurts or turns red, it's time to stop, even with miles left on the plan.
Is tallow or petroleum jelly better for chafing?
Petroleum jelly is the one with evidence behind it, from the American Academy of Dermatology and a 2004 sports medicine review. Both say it reduces friction. A tallow balm is a fat that does the same slip job. I haven't found a study testing tallow against petroleum jelly for chafing, and we haven't run one.
When should chafed skin see a doctor or a dermatologist?
When it's raw or weeping, or when it shows the signs the American Academy of Dermatology lists for a visit: pus, or pain or swelling that grows. A 2014 review in American Family Physician adds that friction and inflammation can break skin down and let fungal or bacterial infections in. If a rubbed spot isn't calmer within a few days, don't wait it out.
Go deeper
Our petrolatum comparison covers how hard petrolatum seals next to a fat, and what is a barrier cream sorts out the protectant creams. Tallow for hands and heels covers the spots that dry out first. The beef tallow for skin guide is where we've put what tallow does on skin, and what it doesn't. Rough arms and keratosis pilaris covers the other body-skin job, and postpartum skin the months when chafing shows up for new parents.
Sources
- American Academy of Dermatology Association (2026). How to prevent and treat blisters, with its chafing tips, last updated July 6, 2026. AAD.
- Kalra MG, Higgins KE, Kinney BS (2014). Intertrigo and secondary skin infections, a review of rashes in skin folds. American Family Physician.
- Sethi A, Kaur T, Malhotra SK, Gambhir ML (2016). Moisturizers: the slippery road. Indian Journal of Dermatology, volume 61, issue 3, pages 279 to 287.
- Derler S, Gerhardt LC (2012). Tribology of skin: review and analysis of experimental results for the friction coefficient of human skin. Tribology Letters, volume 45, pages 1 to 27, January 2012.
- Mailler EA, Adams BB (2004). The wear and tear of 26.2: dermatological injuries reported on marathon day. British Journal of Sports Medicine.
Aspen is the co-founder of Craft Tallow and runs the wear tests: every recipe goes on her skin and the family's for weeks before it gets a label. Questions? Reply to any email from us; it lands with one of us.