Our skin, coupled with our immune system, provides a strong defense against germs that want to harm us. However, sometimes the germs prevail and infection sets in. In this lesson, you’ll become familiar with the terminology for various infections of the skin.

The Skin as a Barrier

Our skin performs many functions, one of which is acting as a barrier. It is Mother Nature’s built-in force field that protects us from many potentially-harmful factors. To name just a few: ultraviolet radiation, freezing temperatures, and bacteria. However, despite this amazing first line of defense, sometimes bacteria are able to penetrate our outer defenses and gain access to our bodies.

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We are going to explore the various skin infections that are a direct result of such bacterial penetrations. In order to do so, we are going to follow the medical journey of a guy named Gus. Unfortunately, Gus is prone to getting pyoderma, or any superficial skin infection in which pus is produced.

The word ‘pyoderma’ is derived from the Greek ‘pyo’, meaning ‘pus’, and ‘derma’, meaning ‘skin’. So as we work through this lesson, poor Gus will develop pus from a variety of infectious skin diseases, ranging in severity from mild to life-threatening.

Boils

Gus awakens one morning to find that his right forearm has a red lump on it. As the day progresses it becomes harder, redder, and more painful. What is wrong with poor Gus? He has a furuncle.

A furuncle, commonly referred to as a boil, is a painful collection of pus under the surface of the skin caused by a bacterial infection. Most often a furuncle begins as a small, red bump. Then, it begins to accumulate pus under the surface, leading to firmness, tenderness, and swelling. A central opening or ‘head’ can be present. It is through this opening that the boil is able to drain, bringing significant relief to the patient when it does.

However, some furuncles do not drain independently. In those instances, a health care professional may prescribe a course of antibiotics. If the furuncle still fails to respond to treatment, then an incision and drainage may need to be performed to empty the pus from the boil.

Luckily for Gus, his furuncle responds quickly to the antibiotics and it does not evolve into a carbuncle. A carbuncle is the collection of two or more furuncles. Even though the furuncles are joined under the skin in a common pool of pus, each maintains its own central opening at the surface.

Localized Skin Infections

Now, we’ll time-travel back to when Gus was the tender age of two. He awakens in his crib, calling for his mommy. When she enters, she sees that Gus has tiny red pimples all around his mouth and nose. Frightened, she rushes him to the pediatrician who informs her that Gus has impetigo.

Impetigo is a bacterial infection, common in younger children, in which multiple pustules form around the mouth and nose. Usually, the child or infant develops pus-filled sores on the face, which then rupture forming a yellowish-brownish crust. This condition is highly contagious and requires antibiotic treatment.

Now, back to the present day! Gus is playing darts with friends. Accidentally, he gets poked by a dart on his hand. Wanting to look macho, he doesn’t wash it or bandage it. The next day, the poke mark is a little red. The day after that his entire arm is red, warm, and starting to swell. What is the diagnosis this time? Cellulitis.

Cellulitis is a superficial bacterial infection of an area of skin. A person will note a particular area of the skin beginning to turn red. The area will then turn hot and swollen, and the clearly-defined redness may spread rapidly. If left untreated, this condition can evolve into the life-threatening disorder known as sepsis, which is when the infection enters the bloodstream. Fortunately, Gus makes it to his doctor, starts a course of antibiotics, and his cellulitis resolves before any complications arise.

However, a few months later Gus is shaving his face and he notices that the razor is dull. Unfortunately, he forgets to pick up new razors on the way back home from work, so the next morning he shaves yet again with the dull razor. The following morning his chin and cheeks are covered in little red bumps and the skin is tender. With a sigh, Gus heads to the clinic where he discovers he has folliculitis.

Folliculitis is a bacterial infection of a hair follicle. The hair follicle lies below the surface of the skin. It is here where the inflammation starts, leading to red bumps or pustules forming around the hair shaft. The affected area can become tender and if the infection is not cleared quickly, permanent hair loss can result. Folliculitis most often affects hairs at the nape of the neck, in the armpits, and on the legs. In men, it can also affect the upper chest and beard region.

Rare Life-Threatening Skin Infections

The last two conditions we will examine differ in their severity. Unlike the previous skin infections, these require rapid identification and treatment or the patient will suffer serious effects.

Necrotizing fasciitis is a life-threatening bacterial skin infection that causes rapid tissue death. Although the condition is most often referred to in popular media as flesh-eating bacteria, there are actually several strains of bacteria that can cause necrotizing fasciitis. In order to treat the condition, it is imperative that it be identified as NF quickly. The difficulty here is that symptoms tend to be vague and are found in multiple conditions: redness of the skin, tenderness, and fever. The most differentiating factor is the severity of the pain in relation to the physical appearance.

So when Gus has a small red bump and the health care provider palpates it, instead of say ‘Oooo’ or ‘That’s tender!’, he screams and jumps off the table. The pain response is NOT proportionate to the clinical presentation. Patients most often need intravenous antibiotics, or within hours, NF can lead to significant tissue loss, organ failure, and death.

Finally, if a bacterial infection is allowed to fester following an injury or illness, gangrene can result. Gangrene is a skin condition in which human tissue dies. The dead tissue that falls away from the gangrenous area is termed eschar.

As the bacteria destroy the skin cells, the area becomes intensely painful and can turn a variety of colors: purple, black, and brown. Ultimately, after the nerve endings are likewise destroyed, the area becomes numb. Remember Gus’ dart wound on his hand? Well, if he had never gone to the doctor but allowed the injury to continue to brew, then he may have developed gangrene.

Gangrene, if identified and treated quickly with antibiotics and removal of the eschar or dead tissue, can be halted. However, if gangrene is left unchecked, the infection will ultimately enter the bloodstream, leading to sepsis and possibly death.

Lesson Summary

In summary, our poor friend Gus has suffered through all of the following:

  • A furuncle: a painful collection of pus under the surface of the skin caused by a bacterial infection, commonly known as a boil
  • Impetigo : a bacterial infection common in younger children, in which multiple pustules form around the mouth and nose
  • Cellulitis: a superficial bacterial infection of an area of skin
  • Folliculitis: a bacterial infection of a hair follicle
  • Necrotizing fasciitis : a life-threatening bacterial skin infection that causes rapid tissue death, commonly known as flesh-eating bacteria
  • Gangrene : a festering bacterial skin infection which results in the death of human tissue

Fortuitously, Gus has been treated by quick-thinking health care providers and efficacious antibiotics! Let’s hope his natural barrier, the skin, can remain intact and deflect any future bacterial invaders.

Learning Outcomes

When this lesson ends, you should be able to:

  • Recognize several different types of infectious skin conditions
  • Define pyoderma
  • Describe those skin conditions that are localized
  • Determine which skin infections are life-threatening