What Is A Bacterial Skin Infection?


What causes bacterial skin infections?

Bacterial skin infections are fairly common even although, in the main, only two bacteria are responsible for causing them:

  • Staphylococcus aureus
  • Streptococcus.

There are other bacteria that can infect, but the two above are the most likely causes.
Firstly, we'll take a closer look at both these bacteria and then find out what specific infections of the skin they may cause.

Staphylococcus aureus

There are several types of staphylococcus bacteria but most infections tend to be caused by staphylococcus aureus, (staph.aureus).

This bacteria is also a frequent companion with humans and can be found on the skin in places such as the armpits, buttocks as well as inside the nose. For the most part they do no harm. However, when the opportunity presents itself then staph.aureus can cause infections. There are two main types:

  • Invasive - this is when the infection is inside the body. Examples are - blood poisoning, endocarditis (an infection of the lining of the heart).
  • Skin - this bacteria can cause infections on the skin such as boils and impetigo among others.


This bacteria can cause various problems ranging from mild infections to severe ones such as pneumonia. There are more than twenty different strains of this bacteria and they are classified into two groups:

  • Group A: the bacteria in this group are usually referred to as 'strep A' for short. They are frequently found on the surface of the skin but also inside the throat. They cause infection in both adults and children. Although the infections from this group are unpleasant they don't normally pose a serious threat to health. Infections caused by strep A include - impetigo, sinusitis, cellulitis, throat infections, inner ear infections. The only time Strep A becomes serious is if it manages to invade deep inside the body to the organs or tissues. Invasive infections such as these would include - pneumonia, meningitis, osteomylitis and necrotising fasciitis.
  • Group B: as with 'strep A', these bacteria are referred to as 'strep B' for short. This bacteria normally lives inside the digestive system and in women the vaginal area where it usually does no harm. This bacteria only tends to affect newborn babies since older humans tend to be able to develop an immunity to it. With newborns this bacteria can cause serious infections such as meningitis and pneumonia.

Let's take a closer look at what particular infections these bacteria can cause on or under the skin.

Staphylococcus aureus under the microscope. This bacteria is responsible for a number of different infections.
Staphylococcus aureus under the microscope. This bacteria is responsible for a number of different infections. | Source

How does bacteria infect the skin?

The skin is always colonised by thousands of bacteria. Most of them are harmless and many are beneficial. The harmless ones however, can become a danger when an opportunity presents itself. Normally this occurs when the protective barrier of the skin is breached through a cut, graze, scrape, puncture wound or some other form of trauma. In addition, certain groups of people are much more likely to develop a skin infection because they already have an existing medical ailment that makes them prone to infections. For example people with diabetes and AIDS or any other condition where the immune system is not fully functional are particularly vulnerable. In addition, people who already have skin conditions such as eczema or wounds, like burns, are also at high risk of developing skin infections.

However, healthy people can also develop skin infections especially if they are careless about hygiene. For example people who work in areas where they are working with materials that have high levels of bacteria - such as poultry and meat - are at risk if hand hygiene in particular is poor.

A bacterial infection called cellulitis that affects the deeper layers of the skin and tissues.
A bacterial infection called cellulitis that affects the deeper layers of the skin and tissues. | Source
A carbuncle showing multiple areas of draining pus.
A carbuncle showing multiple areas of draining pus. | Source
A boil (feruncle) a common form of skin infection
A boil (feruncle) a common form of skin infection | Source

The most common types of bacterial skin infections

There are a number of infections that are fairly common but the list below is not exhaustive. However, is should be enough to demonstrate how versatile bacteria are when causing skin infections.

cellulitis - there are a few causes of cellulitis but one of the main ones is by a strep A group bacteria and also staph aureus. The bacteria affect the underlying skin layers and tissues. When a person suffers from this infection the area can suddenly turn very red, swollen and painful. When touched the area feels hot. People may also experience fever and chills when this type of infection is present.

Cellulitis most often occurs when the bacteria is able to enter the deeper layers of skin through a cut, bite or burn. It can develop in any area of the body but is often found in the legs. In addition, people who have existing skin conditions, such as eczema, that cause small lacerations are more at risk of developing cellulitis. Other high risk groups include people with immune suppression and diabetes. Cellulitis can also become a very serious problem if it causes a secondary infection in the body such as septicaemia.


this is an inflammation or infection of the hair follicles on the skin. Our skin is covered in these follicles and with this infection it is usually one area of the skin that is affected. When the follicles are infected they swell as they begin to fill with pus. Basically they look like small pimples. One of the main causes of this infection is by the staph aureus bacteria. Frequently this condition will be found on areas of the skin where abrasions occur - such as shaving. Alternatively blockage of the hair follicles can also cause this infection to develop.


These are infected lumps on the skin that can occur with healthy people but are usually a one off. It's rare for a child to develop a carbuncle or boil and they tend to be seen more in teenagers and young adults. However older adults can be at risk if:

  • They are obese.
  • If they have a skin condition such as eczema or scabies that cause itching and scratching.
  • A suppressed immune system.
  • If you are a carrier of staphylococcal bacteria.
  • If you have an illness that is making you generally unwell over a period of time.

Carbuncles and boils are related:

  • Carbuncle - these are usually found on the back, the thighs or the back of the neck. They are very hard lumps that are red and painful. Unlike a boil that tends to leak pus from the centre, a carbuncle can leak pus from different areas of the lump. In addition, people usually always feel unwell, have a high temperature and feel exhaustion when they have a carbuncle.
  • Boil (also known as a 'furuncle') - these tend to occur in areas where there is hair growth, sweat and friction such as the armpits, neck, face, buttocks and legs. Staph aureus is the bacteria most likely responsible for a boil. A boil is red lump, usually filled with pus in the centre. They are normally swollen, inflamed and painful. Many of them heal by themselves although this can take up to 3 weeks and don't leave any scarring. Large boils usually need to be drained and a course of anti-biotics given.
  • Chronic furunculosis - this is a particularly nasty condition where crops of boils erupt over a period of time. For some people the boils are a permanent presence with others they only occur from time to time.


This is a skin infection that usually affects children but all ages can develop it.There are two bacteria that can cause this infection:

  • Staphylococcus aureus - this is the bacteria that is most likely to cause the infection.
  • Streptococcus pyogenes

There are two main forms of impetigo:

  • Primary - this is when the bacteria infect healthy skin.
  • Secondary - this is when the infection starts due to another condition such as eczema, psoriasis or on occasion a cut in the skin.

The first indication of impetigo is a rash that normally appears 4-10 days after being infected by the bacteria. Small blisters develop on the skin but they burst rapidly leaving a crusty, scab on the surface of the skin. It is also quite common to see a red, inflamed area just under the crust. Although impetigo can affect any area, the face is the usual location for the infection to develop.

Having looked at the causes and examples of bacterial skin infections, we'll briefly look at the treatments.

The bacteria that can cause skin infections normally live on our skin or other areas of the body and do no harm.
The bacteria that can cause skin infections normally live on our skin or other areas of the body and do no harm. | Source

Treatments for bacterial skin infections

If it's a child that you suspect might have an infection, then get medical advice for them. For all cases of carbuncles medical advice is needed and anti-biotic treatment - normally flucloxacillin - will be given for at least 7 days. For people who are allergic to penicillin based anti-biotics, erythromycin will be given instead. Even when the boil has cleared up, you must continue the full course of anti-biotics as the bacteria, although cleared from the surface, are probably still deeper within the wound area. You should always seek medical help if:

  • You have a boil that is moderate to large size. If it feels soft and spongy to the touch.
  • A carbuncle always requires medical advice no matter what size it is.
  • If you have a boil on your face as this can lead to other complications, some of which may be serious. For example abscesses in some of the major organs, sepsis and others.
  • If you have a high temperature or feeling generally unwell.
  • Another infection develops such as cellulitis.
  • If you have diabetes, HIV, AIDS or any condition that weakens the immune system.
  • If you are having chemotherapy and a boil develops.
  • Even if the boil is small, but it hasn't cleared up after about two weeks.
  • If you are unsure at all about whether it's a boil, carbuncle or something else then speak to your doctor.

Antibiotics are given when:

  • For all carbuncles,
  • High temperature,
  • Secondary infection starts such as cellulitis,
  • If the boil is on your face seek medical help as soon as you can.
  • Face boils do have a high risk of complications setting in.
  • If you have a lot of pain.
  • The boil is large and feels soft and spongy to the touch.

Self treatment for small boils.

If the boil is quite small and not bothering you, apply a warm face cloth to the area for 10minutes about 3 or 4 times a day. The heat increases the circulation to the area so increasing the white blood cells to the location and promotes faster healing. When the boil bursts - don't squeeze or lance it - cover the area with a sterile gauze dressing.

However, if the boil is quite large and/or feels soft and spongy, then go to your doctor as the boil is unlikely to burst on its own and needs specific treatment from a medical professional.


There are many treatments that can be used for this condition that include natural or alternative therapies. With medicine treatment anti-biotics either in tablet or cream form are usually prescribed and the prescription may include an anti-bacterial face wash.

Many of the natural or alternative therapies include herbal remedies and skin preparations.


This infection always requires anti-biotic treatment. In cases where the anti-biotics are not effective, hospital admission is the next step.

Although these infections are nasty, keep in mind that the bacteria causing them live happily and harmlessly on our skins day in and day out without causing any problems. In addition, most of these infections are mild and easy to heal. Having a good hygiene routine, appropriate hand washing, including covering cuts and grazes when they occur are some of the best preventative steps you can take.

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Comments 14 comments

Frank Atanacio profile image

Frank Atanacio 4 years ago from Shelton

my goodness some of the photos are just horrible a great share seeker thank you for the info :) Frank

kittythedreamer profile image

kittythedreamer 4 years ago from the Ether

Always so well written and constructed, are you a doctor? :)

tlpoague profile image

tlpoague 4 years ago from USA

Interesting and informative hub here. I use to work with the elderly and had to be cautious when handling certain one's that had skin abrasions or certain skin problems. This is every helpful information to know. Thanks for sharing it.

actionbronson profile image

actionbronson 4 years ago

Very useful and informative hub. Definitely a good read. I voted thumbs up!

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

LOL!! Hi Frank! Hope I didn't put you off eating!! You're right though, some of the photos are gross!!!

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

Hi Kitty, lovely to hear from you and glad you enjoyed the hub! No, I'm no doctor, just an ex-nurse writing about a few things that I've learned on passing through!! LOL!!

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

Hi tipoague, many thanks for stopping by and glad that you found the hub useful. Yes, the elderly to tend to be very prone to bacterial skin infections and I agree, that it always wise to take precautions!

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

Hi actionabronson, lovely to hear from you and glad that you enjoyed the hub! Many thanks for the thumbs up - greatly appreciated!!

Gypsy Rose Lee profile image

Gypsy Rose Lee 4 years ago from Riga, Latvia

Voted up and interesting. Thanks for a very informative and useful hub. Didn't know there were such skin infections. Passing this on.

AliciaC profile image

AliciaC 4 years ago from British Columbia, Canada

This is a very useful and detailed hub, Seeker7! Thank you for sharing all the great information.

Eiddwen profile image

Eiddwen 4 years ago from Wales

Thanks for sharing this interesting and very useful hub ;have a great weekend.


Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

Hi Gypsy, hope things are well with you - are you all set for Christmas?

Glad that you enjoyed the hub and thanks for the share as always!

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

Hi Alicia, lovel to hear from you and glad that you enjoyed the hub!!

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

Hi Eddy, hope things are well with you - are you all set for Christmas??

Many thanks for the share and glad that you enjoyed the hub!

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