Bacteria on the Skin: Health Benefits and Infections
Bacteria in and on the Body
Many people believe that bacteria living in or on our body must be bad for us. In reality, most of the trillions of bacteria that share our body with us have either a beneficial or a neutral effect on our lives. In fact, it would be difficult to survive if all of our microbes disappeared. Most of the microbes live in our digestive tract, but a large population lives on the skin.
About a trillion microscopic organisms reside on or in the skin. Most of them are bacteria. The majority of these bacteria are harmless. Some are harmless most of the time but can cause a problem under certain conditions. Some may actually be helpful and are thought to boost the activity of our immune system.
The resident bacteria on the skin are sometimes known as the skin flora and are said to form the skin microbiome. They feed on dead skin cells, chemicals released by living cells, and sebum. Sebum is an oily substance made by sebaceous glands. Its chief function is to lubricate and waterproof the skin.
Resident and Transient Bacteria on the Skin
Bacteria on the skin are classified as resident or transient bacteria. Resident bacteria live on the surface of the skin and in its upper layer. They are our long-term companions and aren't removed by washing with soap and water. They can be removed with certain antibacterial chemicals, though. This article focuses on some effects of resident skin bacteria on our lives.
Transient bacteria are those that we pick up when we touch contaminated surfaces. They aren't as firmly integrated with our skin as our resident bacteria and can be removed by washing with soap and water. Transient bacteria are more likely to be harmful than resident ones. When health experts tell us to wash our hands to prevent infections, they are often thinking about the potentially dangerous transient bacteria that may come into contact with our skin.
An NIAID Scientist Describes Good Skin Bacteria
The species of bacteria living on and in our skin depends on the habitat. Dry skin, oily areas, and areas that tend to stay moist (such as the skin between the toes) all contain different bacterial communities. Fungi also live on our skin.
Resident Skin Bacteria May Boost Immunity
Resident skin bacteria are classified as commensals. Commensalism is a relationship in which one organism benefits from the association and the other is unaffected. Mutualism may be a better name for the relationship between skin bacteria and us, however. In mutualism, both organisms benefit from their association.
Recent evidence is showing that bacteria living on the skin may help us. The evidence suggests that some may protect us from pathogens (microbes that cause disease) by stimulating the activity of our immune system and possibly by making antimicrobial chemicals. The immune system's job is to fight disease.
Protection From Leishmania
In 2012, researchers at the National Institute of Allergy and Infectious Diseases (NIAID) performed an interesting experiment in mice. The experiment demonstrated the protective role played by one type of skin bacterium. The mice were germ-free and had no microbes in their gut or on their skin, the most common sites for bacteria in both mouse and human bodies.
The researchers added a bacterium called Staphylococcus epidermidis to the skin of some of the germ-free mice. The bacterium multiplied and colonized the skin of the mice. The researchers then added a protozoan parasite called Leishmania major to the skin of the germ-free mice that had been given Staphylococcus and to the skin of germ-free mice without Staphyloccus. The mice with Staphylococcus were able to fight Leishmania; the mice without Staphylococcus were unable to fight the parasite.
Leishmania is also a parasite on human skin and Staphylococcus epidermidis is part of our skin flora. The researchers suspect that the results of their experiment with mice would be the same if the experiment was performed on human skin. They don't know whether this would be the case, however.
In humans, Leishmania causes a disease called leishmaniasis. The most common type of the disease is restricted to the skin and is called cutaneous leishmaniasis. Visceral leishmaniasis affects the internal organs and is a very dangerous disease.
Protection From a Fungal Infection
In 2015, the same team that studied the relationship between Staphyloccus epidermidis and Leishmania reported another interesting discovery about the bacterium. Once again, the study was performed in mice.
Once Staphyloccus epidermidis had colonized the skin of the mice, the researchers found an increase in the number of CD8+ T cells in their body. These T cells are part of the immune system in both mice and humans. The cells produce signaling molecules that stimulate other cells in the immune system and cause them to spring into action.
After the T cell level had risen, the researchers applied a pathogenic fungus to the skin of the mice. The mice were able to destroy the fungus. If the T cell and signaling molecule levels were reduced, the mice were unable to fight the pathogen.
The information below is for general interest only. Anybody with a skin problem that concerns them should visit a doctor for a diagnosis and treatment recommendations.
One human skin problem caused by bacteria is folliculitis, or inflammation of the hair follicles. A hair follicle is a structure in the skin that produces a hair. It can become inflamed by either a bacterial infection or an irritation. Folliculitis is most common where skin is damaged. Insect bites, shaving cuts, or friction as the skin is rubbed repeatedly against clothing are some ways in which this damage may occur.
Follicuilitis causes groups of small, red bumps to appear on the skin. The skin may also be itchy. If an infection is present, pimples filled with pus may form. Mild folliculitis may not need any treatment. Doctors may prescribe antibiotic creams or tablets for more serious cases.
The video above describes Folliculitis decalvans, a rare disorder in which inflamed hair follicles on the scalp are accompanied by patches of hair loss, or alopecia. The cause isn't known, but it may sometimes be due to an abnormal reaction to Staphylococcus aureus.
Boils and Carbuncles
Like some cases of folliculitis, a boil is produced due to an infection of hair follicles. In this case, however, the infection goes deeper into the skin and a large, painful swelling filled with pus develops over the infected area. Boils are also called furuncles.
The Mayo Clinic says that small boils can "generally" be treated at home. Home treatment includes applying warm compresses to the boil for ten minutes at a time, three or four times a day. When the boil has ruptured, it should be covered with a sterile dressing. It's important to be careful at this stage, since the fluid from the boil contains bacteria which can infect new areas. If a boil is soft, it may not burst on its own. This type of boil requires medical treatment.
A carbuncle is a more extensive infection in which a group of boils forms. It often causes more discomfort than single boils and may be harder to treat.
Impetigo is a very contagious skin infection that is most common in young children. Red sores or blisters may appear on the face—especially around the nose and mouth—and on the neck, hands, forearms, or diaper area. Impetigo may develop on undamaged skin, but it usually appears on skin that has been irritated by being scratched after another injury, such as an encounter with poison ivy.
Large blisters are produced in bullous impetigo while crusted sores are produced in non-bullous impetigo. Non-bullous impetigo is the most common type. Stapyhlococcus aureus can cause either type of impetigo. Non-bullous impetigo may also be caused by a form of Streptococcus.
Impetigo can be spread from one part of the body to another or from one person to another by skin contact. Touching materials like wash cloths, towels, or clothes that have come into contact with the sores can also transmit the disease. Impetigo is often treated with an antibiotic cream or with an antibiotic medication that is swallowed.
Cellulitis is an infection of the tissues below the surface of the skin. It is often treated by antibiotics. It's potentially dangerous, however, because the bacteria may enter the blood or lymph nodes under the skin and then spread through the body. It's important to begin treatment as soon as possible.
Streptococcus and Staphylococcus are common causes of cellulitis. Unfortunately, MRSA (methicillin-resistant Staphylococcus aureus) also causes cellulitis. This bacterium is hard to treat because it's resistant to many common antibiotics, including methicillin. It's a different variety of bacterium from regular Staphylococcus aureus.
Risk Factors for Cellulitis
Factors that increase the risk of cellulitis development include:
- a prior injury that has damaged the skin, making it easier for bacteria to penetrate the deeper layers of the skin
- disorders that weaken the protective barrier of the skin, such as eczema and psoriasis
- certain health problems, such as diabetes and disorders that weaken the immune system
- being an older adult
A Patient With Cellulitis
Possible Symptoms of the Disorder
Possible symptoms of cellulitis include the following:
- The infected area may be red, warm, swollen and tender. These symptoms may occur in other conditions besides cellulitis, but they are a warning sign and should be watched very carefully.
- If the red and swollen area is expanding, see a doctor very soon.
- If the red and swollen area is rapidly getting worse, see a doctor immediately.
- If a fever is present as well as a red and swollen area, see a doctor immediately.
Bacteria and Acne
Propionibacterium acnes is a normal inhabitant of most people's skin. It lives within the hair follicles instead of on the surface of the skin. The bacterium feeds on fatty acids in sebum, chemicals made by cells, and cellular debris. It may also be found in our gastrointestinal tract. Like other bacteria in our body, Propionibacterium acnes is metabolically active. It releases digestive enzymes and other chemicals and alters the environment around it.
Despite its activities, the microbe is usually a harmless member of our bacterial community. However, like some other skin bacteria it may occasionally cause problems. During adolescence the amount of sebum that's made increases as a response to hormonal changes. This may cause a corresponding increase in the population of Propionibacterium acnes. At high levels the bacterium can cause inflammation and play a role in the development of acne.
Like skin bacteria, most bacteria in our intestine are helpful or harmless, but some dangerous bacteria may be present. These can be released in feces. Fecal bacteria can easily be transferred to our hands when we use a toilet or a public washroom. Washing the hands in these situations is therefore extremely important. Washing the hands before eating is also important in order to remove any harmful transient bacteria that we've picked up by touching objects.
It's also necessary to wash the hands after coming into a contact with certain skin problems caused by bacteria. The bacteria are often behaving abnormally or located in an unusual habitat (for them) and can sometimes be transferred from one person to another.
Fortunately, although some bacteria can cause unpleasant or dangerous infections, the majority of the resident bacteria on our skin are friendly. Scientists are making very interesting discoveries about the lives of these organisms and the ways in which they affect us. Skin bacteria may help us in more ways than we realize.
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- "Folliculitis - Topic Overview." WebMD. http://www.webmd.com/skin-problems-and-treatments/tc/folliculitis-topic-overview#1 (accessed September 15, 2017).
- "Boils and carbuncles." The Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/boils-and-carbuncles/home/ovc-20214754 (accessed September 15, 2017).
- "Impetigo." National Health Service. http://www.nhs.uk/conditions/impetigo/Pages/Introduction.aspx (accessed September 15, 2017).
- Dhar, A. Damian, MD. "Cellulitis." The Merck Manual. http://www.merckmanuals.com/en-ca/home/skin-disorders/bacterial-skin-infections/cellulitis (accessed September 15, 2017).
- "Acne." Canadian Dermatology Association. https://dermatology.ca/public-patients/skin/acne/ (accessed September 15, 2017).
Questions & Answers
© 2013 Linda Crampton