Wearing the same underwear for two days might seem harmless, especially if it still looks and smells clean. After all, many clothes can be worn more than once before washing. Underwear, however, is different because it remains in close contact with warm, moisture-prone areas of the body for many hours.

Throughout the day, underwear collects sweat, natural body oils, dead skin cells, and microorganisms normally present on the skin. Even when the fabric appears perfectly clean, moisture and bacteria can remain trapped in it. Wearing the same pair again gives those microorganisms additional time in a warm environment where they can multiply.

The surprising answer is that you technically can wear underwear for two days, but regularly doing so isn’t recommended. For most people, changing into a clean pair every day is the better hygiene habit. It’s especially important after exercising, sweating heavily, swimming, or spending a long day in hot weather.

Repeatedly wearing damp or dirty underwear may contribute to unpleasant odors, itching, chafing, and skin irritation. People who are particularly sensitive to moisture may experience problems sooner than others. Breathable underwear and changing promptly after heavy sweating can help keep the area dry and comfortable.

So forgetting to change your underwear once doesn’t automatically mean something terrible will happen. The concern is making it a regular habit. A fresh pair each day—and another change whenever underwear becomes sweaty or wet—is the simplest approach for maintaining comfort and good personal hygiene.