Skin bacteria. Coloured scanning electron micrograph (SEM) of various bacteria (rod-shapes and spheres) on human skin. Many types of bacteria are found on skin, especially associated with sweat glands and hair follicles. They usually cause no problems, although some can cause acne. Bacteria usually only become a problem if they penetrate the skin, for example through a wound or cut. The two skin cells at centre are squamous cells, flat keratinised, dead cells, that are continuously sloughed off and replaced with new cells from below.