If you notice what looks like pimples, bumps or in-grown hairs on the areas where you shave, you may have "razor bumps". Doctors call this condition Pseudofolliculitis barbae, or PFB. PFB is most common in African American men and others with coarse or curly hair. It's less common in women, but it does occur. PFB is most common on the face and neck where hair is shaved or plucked. But it can also occur in the underarm and pubic areas as well as on the chest, legs or back.
What happens to cause these "razor bumps" is that shaving sharpens the ends of the hair, making it easier for the hairs to curve back into the skin. Stretching the skin while shaving can cause the newly cut hair to retract into the hair follicle. The bumps that you see are caused by skin irritation and inflammation where the hair has re-entered the skin.
There are several things you can do to help minimize razor bumps while shaving. Some doctors recommend using only electric shavers which don't give quite as close a shave, whereas double or triple-edged razors give extra-close shaves that may make the hair more apt to re-enter the skin. If you do use a blade, wash with a mild cleanser and warm water before shaving. This will help soften the hairs and help prevent a sharp edge that can enter the skin after shaving. Massaging the area to be shaved with a warm washcloth can help free the hairs and make them easier to cut. Avoid stretching the skin while shaving and shave in the direction of hair growth to minimize irritation. Dermatologists recommend using a shave gel for sensitive skin containing moisturizing lubricants such as AVEENO® Skin Relief Shave Gel. Shave every other day and use a razor specially made for ingrown hairs.
Source: Perry PK, Cook-Bolden FE, Rahman Z, Jones E, Taylor SC. Defining pseudofolliculitis barbae in 2001: A review of the literature and current trends. J Am Acad Dermatol 2002;46:S113-9.