These are also known as "hair muscles". These are tiny muslces that are attached to the hair shaft. These muscles cause the hair to stand up or be erect. When the Arrector Pili muscles contract due to stress, fear or other nervous conditions, the hair becomes stiff and will actually "stand on end".
Daily Hair Tip
Choose hair care products to suit your specific hair type. Be willing to try several brands until you find a hair care product line that makes your hair look and feel fabulous. Recognize that all hair care products don't always work well on all hair types.