Since you’ve been hitting the gym regularly, your biceps are growing and your belly is flattening.

But there might be one not-so-attractive physical consequence of your gym sessions: tiny, red bumps that sprout up on your shoulders, the edges of your armpits, and around your groin. They look like acne, and they very well might be. But they could also signal a skin condition called miliaria, also known as heat rash.

Related: 5 Nasty Contagious Skin Conditions You Can Pick Up At the Gym

Acne and miliaria look pretty similar, but they have different causes—so if you use treatment meant for one, it won’t help you at all if you’re actually suffering from the other.

What’s the Difference Between Acne and Heat Rash?

First, the similarities: Acne and heat rash can both crop up when your pores get clogged and irritated.

But acne—which is much more common that miliaria—develops when a pore’s oil duct get blocked with dirt or dead skin cells, says Dr Bruce Robinson, a New York-based dermatologist and fellow of the American Academy of Dermatology.

Bacteria gets trapped in the duct, sparking irritation and inflammation, which makes the pimple red and tender (Whiteheads and blackheads, which also count as acne, are just trapped dirt or dead skin cells without any bacteria or inflammation.) On the other hand, miliaria, or heat rash, forms when a pore’s sweat duct gets clogged with sweat, which forms small clear or red bumps, which resemble a rash.

Related: 5 Hidden Causes Of Acne

Deeper blockages tend to become inflamed, making the bumps look red, Dr. Robinson says. That inflammation can also make them feel itchy or prickly. It’s actually pretty easy to tell zits and heat rash apart if you know what you’re looking for: Pimples are usually larger with a white, pus-filled center, and you might just get one or two in a given area.

Milaria are tiny and appear in clusters, resembling more of an itchy rash, says Dr. Robinson.

Why Do You Get Acne or Heat Rash After Exercising?

Working out is a major trigger for both acne and heat rash: The more you sweat, the greater the chance that dirt or dead skin cells—or sweat itself—could clog your pores and cause a blockage, says Dr. Robinson.

So avoid hanging out in your sweaty workout clothes before changing or showering. Exercising in a damp or humid environment can up the risk for heat rash even more, since high humidity makes it harder for sweat to evaporate off your skin.

Related: 6 Ways to Cover Up Acne Scars

How Can You Prevent Acne or Heat Rash?

Neither a pimple nor heat rash is harmful, and both usually clear up on their own within a few days, says Dr. Robinson. Unless they’re bothering you or you want to try a new treatment, you don’t need to see a dermatologist.
But they can be ugly and annoying, especially if your pimple is sensitive or tender, or your heat rash is itchy.

So play the prevention game for both health conditions: Try toweling off with a wet cloth periodically throughout your workout, Dr. Robinson recommends.

This will remove dirt, grimy buildup, or sweat from your skin’s surface, so it can’t clog your pores and cause pimples or heat rash. And get out of your sweaty clothes and take a shower as soon as you’re finished exercising, to prevent dirt or sweat from getting trapped in your pores, Dr. Robinson says.

Related: Beat Acne with Antioxidants

Take frequent breaks if you’re exercising in the heat, or hot, humid environments, like a sweaty gym. Drinking some cool water or finding a breeze gives yourself a chance to cool down, allowing sweat to evaporate without clogging your pores, Dr. Robinson says. And make sure your exercise clothes aren’t too tight. Loose clothing helps your sweat evaporate, too.

How Can You Treat Acne and Heat Rash?

If you’ve noticed pimples popping up after a workout, acne-fighting body washes that contain ingredients like benzoyl peroxide or salicylic acid can help with treatment, says Dr. Robinson.Look for kinds like that contain 2 percent salicylic acid or 5 to 10 percent benzoyl peroxide. But talk to your dermatologist before using them, since they can irritate your skin, Dr. Robinson says.

As for miliaria, there’s not much you can do to make the blemishes go away any sooner. But if they’re itchy, try an over-the-counter anti-itch cream or lotion. In either case, call your doctor if you notice any pain or swelling, or if your heat rash has any pus. Those symptoms could be signs of infection.

Originally published on menshealth.com