After spending a few nights at a friend’s older apartment, everything seemed perfectly normal at first. But within a couple of days, dozens of small, itchy red bumps began appearing on the arms, legs, and other exposed areas of the body. At first, it seemed like a mild allergic reaction, but as more bumps appeared overnight, it became clear that something in the apartment might be responsible.

One of the most common explanations for clusters of itchy red bumps after sleeping in an unfamiliar place is bed bug bites. Bed bugs are tiny insects that hide in mattresses, bed frames, furniture, and cracks in walls during the day before feeding at night. Their bites often appear in groups or lines on exposed skin, although not everyone reacts to them in the same way.

However, bed bugs are not the only possible cause. Fleas, mosquitoes, mites, allergic reactions to detergents, contact with certain plants, or other skin conditions can produce similar-looking rashes. Because many skin problems resemble one another, it can be difficult to determine the exact cause based on appearance alone.

If you suspect bed bugs, inspect the mattress seams, pillows, headboard, and nearby furniture for tiny insects, dark spots, shed skins, or small white eggs. Washing clothing and bedding in hot water and drying them on high heat can help eliminate any insects that may have traveled home with your belongings. Persistent infestations usually require professional pest control.

If the rash continues to spread, becomes painful, shows signs of infection, or is accompanied by fever, swelling, or difficulty breathing, seek medical attention promptly. While many insect bites improve on their own, identifying the underlying cause is the best way to prevent further exposure and ensure the appropriate treatment.