This is the final post in a three-part series on the microorganisms that live on our skin. In this post, we’ll be talking about where the different skin bacteria live on our bodies.

The skin has many different kinds of bacteria living on it. These are commensal organisms that get nutrition from your skin cells and secretions. For example, Cutibacteria are unique for their ability to feed on the sebum that is produced by your body, helping to regulate the amount you produce and effectively helping to reduce the appearance of acne. These different kinds of bacteria also help to protect your skin from pathogenic infections and will even ward off transient bacteria from outside sources.

However, the amount and types of bacteria on our skin will differ depending on the area. This is because different kinds of bacteria require different kinds of nutrients. As such, the availability of these nutrients and moisture will dictate where some of these microorganisms thrive. For example, the previously mentioned Cutibacteria will only live in areas that actively secrete sebum. This means that they are usually found in areas such as the scalp, the face, and the back.

The bacteria that live in this organ can be categorised into three different areas; oily areas, dry areas, and moist areas.

Oily areas, also known as sebum-rich areas, often refer to areas where there is a lot of hair (and sebaceous glands). This can include the back, the scalp, the face, and sometimes the chest.

Dry areas include the feet, legs, hands, and forearms. These areas have the most diverse bacteria because they’re exposed to the environment. We use these parts of our body to touch things and interact with the world around us, so it’s natural to see more bacteria in these areas.

Moist areas include most of the folds in our skin. This includes the crook of the below, between the toes, in the groin, beneath the breasts and the axilla.

These are the three main categorisations when it comes to areas of the skin where you’ll find certain types of bacteria.

Betaproteobacteria

Betaproteobacteria is a class of Gram-negative bacteria with over 75 genera and 400 species. These bacteria are often found in dry areas of the skin. This means you’ll find it in areas that are often exposed to the elements such as your hands, arms, legs, and feet. The highest concentration of beta proteobacteria is often found in the buttocks, the hands, and the forearms.

Cutibacteria

Cutibacteria is a gram-positive and anaerobic genus of bacteria that is known for its ability to synthesize propionic acid. It typically lives around the hair follicles and sebaceous glands, making it the most common type of bacteria to live on oily parts of the body. This means you’ll find it in your scalp and other areas with a lot of hair. The highest concentrations of Cutibacteria are usually found on the back and in creases around the face such as behind the ears, around the nose, between the eyebrows.

Corynebacteria

Corynebacteria is a gram-positive and aerobic genus of bacteria that are usually not pathogenic but are considered opportunistic. Corynebacteria are most commonly found in the moist regions of the body such as the groin and other folds in the skin. Corynebacteria numbers are usually high around the groin, behind the ears, and also between the toes. Cutibacteria and Corynebacteria are both a part of the Actinobacteria phylum.

Staphylococci

Staphylococci is a gram-positive genus of bacteria that includes around 40 different species with 9 of them having 2 subspecies. They are usually found in moist skin regions like the crook of the elbow, between the toes, and the crook of the knee. The highest concentrations of Staphylococci are often at the base of the heel, the crook of the knee and elbow, and the back of the head.

The concentration of different bacteria around the body can vary greatly from one individual to another, meaning it’s difficult to say where the highest concentration of a specific bacteria is. However, this should give you a good idea of where these bacteria thrive and why they are present in specific areas of the body.

As part of the microbiota that lives on our body, there are also various viruses and fungi that are present on our skin.

Malassezia

Malassezia is the most common genus of fungi found on the surface of our skin. Malassezia requires fat in order to grow, so it’s most commonly found in areas where there are sebaceous glands such as the scalp and upper part of the body. When Malassezia grows too quickly, it can cause itching and the rapid renewal of cells. These are the fungi responsible for conditions such as dandruff.

Viruses

Initial research has shown that circoviridae, papillomaviridae, and polyomaviridae are the most common families of DNA viruses that can be found on the skin. Unfortunately, due to limitations in the techniques that are used to identify viruses in our microbiome, there currently isn’t much information on this topic.

And this concludes our mini three-part series on the microorganisms that live on our skin. There are many different kinds of bacteria that we live in harmony with. However, they can quickly turn on us as well if there’s an opportunity for them to penetrate our skin and infect the inside of our bodies. If they’re able to reach your bloodstream, it can cause a systemic infection which can lead to serious complications.

However, for most healthy people, the bacteria on our skin will only cause minor challenges or difficulties that can typically be dealt with using the right skincare products and by taking good care of our immune system. In fact, many of these bacteria can be beneficial to our skin and will treat you well if you look after your skin.