Hair can appear curly in the morning for several reasons, including sweating at night, restless sleep and the use of certain bed linens. Sections of curly hair are one characteristic of "bed head," the unkempt appearance of hair after sleep.
Because some hair reacts to moisture such as sweat or humidity by curling, sweating at night can lead to curls or frizz in the morning, especially in sections of hair that spend time pressed against a pillow. Tossing and turning contributes to bed head, as movement at night causes the hair to become increasingly tousled and messy. Rougher bed linens can snag hair at night, making curls and bed head more likely. Sleepers can avoid this by using linens made of silk or other slippery materials.