Underarm Chafing: Why It Happens and How to Prevent It

Underarm chafing can start as something barely noticeable.

A little rubbing.

A little warmth.

Then, after hundreds or thousands of arm swings, that small friction point can turn into a painful patch of irritated skin.

It is especially common during running, walking, hiking, gym workouts and hot-weather activity because the underarm area combines several things chafing loves:

• Repeated movement
• Skin-on-skin contact
• Clothing contact
• Heat
• Sweat
• Limited airflow

The good news is that once you know where the friction is coming from, underarm chafing is often much easier to prevent.

What Causes Underarm Chafing?

Chafing happens when repeated friction irritates the outer layer of the skin.

Under the arms, that friction usually comes from one or more of these:

• Upper arm rubbing against the side of the chest
• Skin rubbing against skin
• Shirt or tank-top seams
• Sports bra edges
• Tight armholes
• Hydration vest straps
• Wet fabric
• Repeated arm movement

The armpits are also naturally warm and prone to moisture, which can make friction worse.

Cleveland Clinic specifically identifies the armpits as one of the common areas where chafing occurs and notes that body moisture and wet clothing can increase the chance of irritation.

Why Does Running Cause Underarm Chafing?

Running creates thousands of repetitive arm movements.

With every stride, your arms move forward and backward.

If the inner upper arm touches your torso—or if clothing repeatedly moves across the same patch of skin—that friction keeps happening over and over.

A shirt or sports bra may feel completely comfortable when you start.

But after an hour of movement, sweat and repetition, a small friction point can become much more noticeable.

Runner's World describes chafing as commonly coming from either skin-on-skin or fabric-on-skin rubbing and notes that sweat and rain can make it worse.

Underarm Chafing Isn't Just a Running Problem

Running is a common trigger, but underarm friction can happen during almost any repetitive activity.

That includes:

• Walking
• Hiking
• Strength training
• Rowing
• Cycling
• Sports
• Hot-weather work
• Travel
• Long days in sleeveless clothing

It can also happen when carrying gear.

A hydration vest or backpack strap that sits close to the underarm can create another source of repeated rubbing.

So the real issue is not running itself.

It is repeated friction in the same place.

Common Signs of Underarm Chafing

Early chafing may feel like:

• Warmth
• Mild burning
• Tenderness
• Stinging
• Itching
• Redness

If the rubbing continues, the skin may become increasingly irritated or raw.

That is why it helps to act when you first notice a recurring friction area rather than waiting until it becomes painful.

Why Sweat Makes Underarm Chafing Worse

Your underarms already tend to be warm and moist.

Exercise adds more sweat.

Moisture can make clothing stick, bunch or move differently against the skin. It can also make already-friction-prone skin more vulnerable to repeated rubbing.

Cleveland Clinic recommends moisture management as one strategy for reducing chafing risk, including moisture-wicking clothing and changing out of wet clothes.

This becomes especially important during:

• Summer running
• Humid weather
• Long races
• Rain
• Hiking
• Extended workouts

The longer you stay wet and moving, the more opportunity friction has to build.

How to Prevent Underarm Chafing

The best strategy is usually a combination of reducing unnecessary rubbing and protecting areas where friction is difficult to avoid.

1. Look at Where the Friction Is Coming From

Start by identifying the actual contact point.

Is your:

• Arm rubbing against your torso?
• Shirt seam rubbing the armpit?
• Sports bra edge rubbing?
• Tank top armhole rubbing?
• Hydration vest touching the area?

The solution depends on the source.

Skin-on-skin rubbing may require a different adjustment than a rough seam or poorly positioned strap.

2. Check Your Shirt or Tank Fit

Clothing that is too loose can repeatedly move across the skin.

Clothing that is too tight can create pressure along seams or armholes.

Pay attention to:

• Armhole size
• Seams
• Fabric texture
• Tags
• Bunching
• How the shirt changes once wet

The clothing does not necessarily need to be tighter or looser.

It simply needs to stay in place without repeatedly rubbing the same spot.

3. Choose Moisture-Wicking Fabrics

Technical fabrics that move moisture away from the skin can help prevent clothing from remaining excessively wet during activity.

Heavy cotton can hold sweat and become increasingly uncomfortable during long efforts.

For running, hiking and workouts, lightweight moisture-wicking fabrics are generally a better choice when chafing is a recurring problem.

4. Check Your Sports Bra

Sometimes what feels like underarm chafing actually starts at the edge of a sports bra.

The side panel, strap or seam may sit close enough to the armpit to repeatedly rub during arm movement.

If the irritation follows the edge of your bra, read our [Sports Bra Chafing Guide →].

5. Check Hydration Vests and Backpack Straps

Trail runners and hikers should pay particular attention to gear.

A hydration vest that fits well while standing may shift once:

• Bottles are filled
• The pack is loaded
• Clothing becomes wet
• You start running downhill

If a strap or edge repeatedly touches the armpit, adjust the fit before a long effort.

Gear movement can create friction just as easily as clothing.

6. Reduce Friction Before Activity

If your underarms regularly chafe in the same place, protect that area before movement starts.

Anti-friction products help create a smoother interface between skin, clothing and gear.

Common formats include:

• Petroleum jelly
• Balms
• Anti-chafe sticks
• Creams
• Roll-ons

Runner's World and Cleveland Clinic both include lubricating or anti-chafing products among common prevention strategies.

The important part is timing.

Apply protection before the friction becomes painful.

Where Should You Apply Anti-Chafe for Underarms?

Do not think only about the center of the armpit.

Look at the complete friction area.

Common application zones include:

• Inner upper arm
• Side of the chest
• Edge of the armpit
• Sports bra edge
• Shirt or tank-top armhole contact point
• Hydration vest contact zones

Apply a thin, complete layer anywhere repeated rubbing normally occurs.

What Should You Look for in an Underarm Anti-Chafe Product?

The underarm is a relatively small area with a lot of movement.

Useful product characteristics may include:

• Easy, precise application
• Lightweight feel
• Low mess
• Sweat resistance
• Comfortable feel under clothing
• Ability to cover narrow friction zones

Some people prefer solid sticks or balms.

Others prefer a liquid or roll-on format that can follow the exact edge of the friction area.

Where Run Slick Fits

Underarms were one of the obvious friction areas Run Slick was designed to handle.

The roll-on format makes it easy to apply directly along:

• The inner upper arm
• Side of the chest
• Armpit edge
• Shirt or sports-bra contact lines

Run Slick uses a lightweight silicone-based formula designed to leave a smooth, silky layer rather than a heavy or greasy coating.

Apply a thin layer to clean, dry skin before activity.

Give it a moment to settle before getting dressed or putting on gear.

For very long, wet or high-friction efforts, reapply only if needed.

[Shop Run Slick →]

Underarm Chafing in Hot and Humid Weather

Hot weather deserves special attention.

More heat usually means:

• More sweat
• Wetter clothing
• Longer moisture exposure
• More opportunity for fabric to stick or shift

If you know underarm friction is a problem for you, hot and humid conditions are not the time to test whether you can skip prevention.

Protect known hot spots before the workout begins.

This is particularly important during long summer runs, hikes and races.

Underarm Chafing From Walking

Walking can create the exact same friction pattern as running.

For some people, the arm repeatedly brushes against the torso with every step.

Over several miles—or an entire day of sightseeing, travel, theme parks or outdoor activity—that repetition can add up.

You do not need to be running fast or training for a race to experience underarm chafing.

If the rubbing repeats long enough, friction can become irritation.

Underarm Chafing From Shirts and Tank Tops

Sometimes the problem is not skin-on-skin friction at all.

Check the edge of the clothing.

Common culprits include:

• Rough seams
• Large armholes
• Tight armholes
• Stiff fabric
• Wet fabric
• Tags or stitching

If the chafing follows a straight line or matches the edge of the garment, clothing may be the primary cause.

Try a different cut or fabric before assuming you need more product.

Friction protection can help, but fixing the source of unnecessary rubbing is even better.

What If Your Underarms Are Already Chafed?

Once the skin is already irritated, the goal changes.

You are no longer trying to prevent friction.

You are trying to stop additional irritation and allow the skin to recover.

For mild chafing:

• Stop or reduce the rubbing when possible
• Gently clean the area
• Pat it dry rather than rubbing it
• Avoid clothing or gear that continues irritating it
• Allow the area time to recover

Run Slick is designed to help reduce friction before chafing develops.

Do not apply it to broken, bleeding or severely irritated skin.

If the area becomes increasingly painful, develops open sores, shows signs of infection or does not improve, speak with a healthcare professional.

Underarm Chafing vs a Rash

Not every irritated armpit is chafing.

Friction-related chafing usually makes sense in the context of repeated rubbing.

But irritation in the underarm can also have other causes, including reactions to deodorants or skin-care products, shaving irritation and various skin conditions.

If irritation appears without an obvious source of friction, repeatedly returns, spreads, becomes very itchy, develops unusual bumps or does not improve, consider getting medical advice rather than assuming it is chafing.

Quick Pre-Run Underarm Chafing Checklist

Before a long run, hike or workout, ask:

• Have my underarms chafed before?
• Is my shirt or tank top already tested?
• Are any seams touching a known hot spot?
• Is my sports bra rubbing near my armpit?
• Is my hydration vest positioned correctly?
• Is it going to be especially hot or humid?
• Have I protected the areas that normally rub?

Thirty seconds before you start can make a big difference several hours later.

Frequently Asked Questions

Why do my armpits chafe when I run?

Running creates repeated arm movement. If the inner arm rubs against the torso, clothing, a sports bra or gear thousands of times, that friction can irritate the skin.

Does sweat cause armpit chafing?

Friction is the underlying issue, but sweat and moisture can make chafing more likely by keeping skin and clothing wet and increasing repeated rubbing.

Why do my underarms chafe even when I am walking?

Walking still involves repeated arm movement. Over enough time or distance, the same small contact point can rub thousands of times.

Can deodorant cause underarm chafing?

Deodorant itself is not necessarily chafing, but some products may irritate sensitive skin. If the irritation occurs even without repeated rubbing, consider whether another skin reaction may be involved.

What can I put on my underarms to prevent chafing?

People use products such as petroleum jelly, balms, anti-chafe sticks and silicone-based roll-ons to reduce friction. The best choice depends on your skin, clothing and personal preference.

Can I use Run Slick on my underarms?

Yes. Underarms are a common Run Slick application area. Roll a thin layer onto clean, dry skin wherever rubbing usually occurs and allow it to settle before dressing.

Should I apply anti-chafe before or after running?

Apply friction protection before activity if you know the area tends to rub. Anti-chafing products are more useful for prevention than for treating already-damaged skin.

The Bottom Line

Underarm chafing is usually not random.

Something is rubbing.

Your skin.

Your shirt.

Your sports bra.

Your hydration vest.

Or some combination of them.

Find the friction point.

Fix unnecessary movement when you can.

Prepare for sweat and heat.

And protect the areas that still have to rub before irritation starts.

For a broader look at friction during running, read our [complete guide to preventing chafing while running →].

Hard is okay. Unnecessary friction isn't.

If it rubs, Run Slick on it.™

[Shop Run Slick →]