The average human sheds thousands of dead skin cells per minute, and since you spend one-third of your time in bed, this debris can add up. This attracts dust mites to your bed. A warm or humid atmosphere will make them multiply. If your sheets trap moisture, they’ll develop mold and bacteria in time. Dust mites, pet hair, mold, and other allergens are all factors that trigger allergies. It is recommended to wash your sheets regularly (in hot water) and use hypoallergenic sheets to reduce allergy symptoms.