Your body is covered with microbes, inside and out. It might sound gross, but this is perfectly normal. Our bacterial cells far outnumber our human cells and research is showing that the more diverse those bacterial cells, the healthier we are. Here are some of the most common microorganisms that reside on our skin:
Propionibacteria are the most prevalent on sebaceous, or oily skin, such as nostrils, scalp, upper chest and back. They are lipophilic anaerobes, decomposing oily sebum secreted by our glands to produce propionic acid. Although they are present in infants and babies, they become more prevalent around the onset of puberty, as the sebaceous glands increase their output. One of the bacterial strains, Propionibacterium acnes, is thought to be responsible for inflammation of the glands that can lead to acne.
Staphylococci have their name derived from Greek word for grape, as their colonies resemble grape clusters. They reside predominantly in the moist areas of the body, such as the armpit, the elbow crease, etc. As aerobic bacteria, they produce lactic acid that lowers the pH of the skin and controls growth of other microorganisms. They are particularly prevalent on the skin of babies and infants, their relative abundance decreasing with age. While normally harmless, certain species of staphylococci, such as S. aureus, can act as human pathogens. Methicilin-resistant S. aureus (MRSA) infections are a difficult public health problem in hospitals and beyond.
Corynebacteria are rod-shaped and mostly innocuous. They also prefer moist environments, such as the navel or back of the knee. They grow slowly, even when food is abundant.
Betaproteobacteria are a diverse group, which includes Nitrosomonas, currently excluded from human skin. They are the most prevalent group in dry areas such as the forearms. These bacteria are also the bacteria that dog owners have the most in common with their dogs
Malassezia are actually fungi and get an honorable mention. They are found on our skin in large quantities and are typically harmless. However, certain species can cause dandruff or skin discoloration.