What Is a Rash Guard and What Is It For in Combat Sports?

The essentials in 30 seconds

• What it is: a fitted top in polyester and elastane, with short or long sleeves.
• Where it's worn: no-gi BJJ, grappling, wrestling, MMA, and under the gi for women in competition.
• What it's for: protecting the skin, staying clean on the ground, giving nothing to grab, drying fast.
• What it isn't: a regular sports t-shirt, which billows, rides up, and gets grabbed on the 1st exchange.

What a rash guard does on the mat

Protecting the skin

On the ground, skin rubs constantly against the mat and against your partner. Elbows, shoulders, and forearms take mat burn and scrapes. A rash guard acts as a shield: the fabric slides where skin would catch.

Limiting direct contact

A whole club rolls across the same mat every night. A rash guard reduces the surface of skin exposed to the mat and to other people's sweat. It doesn't replace basic hygiene (showering, short nails, covered cuts, gear washed after every session), but it adds to it.

Giving nothing to grab

In no-gi, grabbing clothing isn't allowed. A loose t-shirt still gets caught under an arm or in a hand. A well-fitted rash guard sticks to the body: there's nothing to grab, nothing that rides up over your face during a sweep.

Staying dry and free to move

Polyester barely absorbs water. Sweat passes through the fabric and dries fast, where cotton soaks it up and gets heavy. Elastane follows every movement without restricting the shoulders or hips.

What a good rash guard is made of

Rashu rash guards are cut from a 230 g/m² fabric, with 4-way stretch, flat seams, and a design dyed into the fibre.

Rash guard or compression shirt: the difference

The two look alike: same fabric family, same close-to-body cut. At Rashu, they don't play the same role.

• The rash guard is the combat piece: a full illustrated design across the whole surface, built for the mat and the cage. It's the top you wear on the ground, in sparring and in open competition.
• The compression shirt is a technical base layer: plain, understated, worn alone at the gym or under other gear.

In short: if you're stepping onto a mat, get a rash guard. If you want a discreet base layer for weightlifting or cardio, get a compression top.

Short sleeves or long sleeves

To go further on BJJ, read our guide to choosing a jiu-jitsu rash guard.

What competition rules say

• IBJJF and AJP, no-gi: a tight-fitting top, long enough to cover the torso down to the shorts, in a black, white, or black-and-white base, with at least 10% of your belt colour. A top entirely in the belt colour is also accepted. Short and long sleeves are both allowed.
• IBJJF, gi: the rash guard under the jacket is mandatory for women and banned for men.
• ADCC: open attire. Any design is allowed, as long as it has no pocket, no zipper, and no hard piece.
• UWW grappling: a red or blue rash guard depending on your corner, at least 60% of the assigned colour.
• UWW amateur MMA: a rash guard is mandatory, short sleeves above the elbow, at least 70% red or blue.

A rash guard illustrated across the whole surface is therefore perfect for training, ADCC, and most opens, but not for IBJJF no-gi. Always check the rulebook of the tournament you're entering before signing up.

Sources: IBJJF uniform rules, ADCC uniform FAQ, UWW rules, reviewed on 2026-10-23.

How to choose your rash guard

1. Your discipline: BJJ and grappling, see the BJJ rash guard collection; MMA, see the MMA rash guard collection.
2. Your cut: men's rash guard or women's rash guard, cut differently at the shoulders, chest, and hips.
3. Your sleeves: based on your discipline and rulebook (see above).
4. Your size: measure your chest and follow the size guide. The rash guard should hug the body without restricting your breathing.
5. Your design: it's your fight gear, it should look like you. Every model is in the rash guards collection.

Care: the 4 rules

• Wash at 30°C max, inside out.
• Never use fabric softener: it clogs the fibre and holds onto odours.
• Air dry, never in the tumble dryer.
• Take the rash guard out of your bag as soon as the session ends.

Full detail is on the rash guard care page.

Our verdict

If you spend time on the ground, a rash guard isn't optional: it's your work gear. Get it fitted, long enough, in a sturdy fabric with flat seams, with a design dyed into the fibre. And save the compression shirt for the gym.

Frequently asked questions

Rash guard or rashguard: which spelling?

Both are used. The term comes from the English "rash guard", literally a guard against rashes. It's often written as one word, "rashguard", and called a "lycra" in some clubs.

Do you need to wear anything under a rash guard?

No, it's worn directly on the skin. Women often add a sports bra underneath.

Does a rash guard replace the gi?

In no-gi, yes: the rash guard and shorts (or spats) make up the whole kit. In gi BJJ, it's worn underneath, and only mandatory for women in IBJJF competition.

How long does a rash guard last?

Years of training if it's washed cold, with no fabric softener, and air dried. Heat is its 1st enemy: it wears out the elastane.

Can you wear a rash guard for weightlifting or running?

Yes, but a plain compression top is often better suited. We compared the two in our article on running in a rash guard.