That small “pocket” in the crotch of women’s underwear isn’t actually a pocket. It’s called a gusset, a second layer of fabric sewn into the crotch area for hygiene, comfort, and breathability. The reason it looks like a pocket is that many manufacturers leave one end unsewn, which creates an open flap. That’s a manufacturing shortcut, not a design feature you’re meant to use.
What the Gusset Actually Does
The gusset serves as a protective barrier between your body and the outer fabric of the underwear. It’s almost always made from cotton or a cotton blend, even when the rest of the underwear is synthetic. Cotton can absorb up to 27 times its weight in water, which makes it effective at wicking away moisture and sweat throughout the day. That matters because the vulvar area is warm and prone to moisture buildup, which creates conditions where bacteria and yeast can thrive.
By keeping things drier and allowing airflow, the cotton gusset helps reduce the risk of yeast infections, urinary tract infections, and general irritation. It also acts as a buffer against the dyes and chemicals in synthetic outer fabrics, which can trigger allergic reactions in people with sensitive skin.
Why One End Is Left Open
The pocket-like opening exists because manufacturers sew the gusset along the leg hole seams on both sides but leave the front (or sometimes back) edge unstitched. This keeps internal seams tucked away so they don’t rub against your skin and cause chafing. It also reinforces the crotch area, which takes the most friction and stress during wear, helping prevent tearing over time.
Cost plays a role too. Sewing both edges closed requires an additional step in production. Leaving one side open is faster and cheaper. Some higher-end brands do sew the gusset fully closed on all sides for a more finished feel, but functionally, it works the same either way. You don’t need to worry about whether yours is open or closed.
Not All Underwear Has One
Most everyday styles like briefs, bikinis, and hipsters include a gusset because they’re designed for all-day wear. But you won’t always find one in specialty underwear. Seamless styles sometimes skip it to maintain a smooth, invisible profile under clothing. Lingerie and crotchless designs often leave it out because they’re not intended for extended wear. If the underwear itself is already made entirely from cotton, it may not need the extra lining at all since the outer fabric already provides breathability.
Thongs and other minimal styles vary by brand. Some include a narrow gusset, while others don’t have enough fabric to support one.
Why Cotton Matters More Than You’d Think
A cotton gusset in otherwise synthetic underwear is better than no gusset at all, but it has limits. Cleveland Clinic notes that a small cotton panel doesn’t fully protect you from the surrounding synthetic fabric and won’t breathe as well as underwear made entirely from cotton. Synthetic materials tend to trap heat and moisture against the skin rather than absorbing it, which can contribute to discomfort and odor over time.
If you’re prone to yeast infections or irritation, choosing underwear that’s 100% cotton (not just cotton-lined) makes a meaningful difference. The gusset alone covers only a small area, while synthetic fabric on either side can still restrict airflow and hold moisture against the skin. For everyday wear, especially in warm weather or during exercise, fully cotton underwear gives your body the best chance to stay dry and balanced.
A Note on Shrinking Gussets
If you’ve noticed gussets getting smaller or narrower in recent years, you’re not imagining it. As underwear cuts have shifted lower on the hip and higher on the leg, the gusset has shrunk along with them. Since the gusset is sewn along the leg hole seams, a higher-cut leg opening means the gusset starts in a different position and may not fully cover the area it’s supposed to protect. Repeated washing can also cause cotton gussets to shrink further, especially if the outer fabric is a synthetic that doesn’t shrink at the same rate. The result is a lining that rides up or barely covers the intended area. When shopping, it’s worth checking that the gusset is wide enough to actually do its job rather than just existing as a token strip of cotton.