7 Signs of Cellulitis (Infection Under the Skin)

Cellulitis is a potentially serious infection of the tissue under the skin (subcutaneous tissue). Even a small break in the skin, like with an insect bite, can lead to cellulitis if bacteria can gain entry into the deeper tissue under the skin. Once in this deep tissue, the infection can sometimes rapidly spread throughout the body. This can be deadly if not treated promptly.

Read more on what is cellulitis.

What Happens In Cellulitis?

The skin is relatively tough barrier that protects the internal environment of the body. However, it is not impervious to injury. Sometimes an injury can cause a break in the skin which then allows microbes to enter the deeper tissue. This can cause an infection which could spread deep into the body as well as to other parts of the body.

The skin is made up of three, not two, layers. The epidermis  is the outermost layer and the dermis lies underneath it. The subcutaneous tissue (hypodermis) lies below the dermis. Impetigo is an infection of the most superficial layers of the epidermis. Deeper epidermal and dermal infections are known as erysipelas.

Cellulitis is an infection of the deeper tissue (subcutaneous tissue or hypodermis). Sometimes it may arise as a complication of impetigo or erysipelas when the infection spreads from the outerlying areas to the deeper skin tissue. At other times a deep injury can implant microbes directly into the subcutaneous tissue

The immune system responds against the presence of these microbes, usually bacteria, in the subcutaneous tissue. However, the immune defenses are sometimes not able to eradicate the bacteria and the infection establishes itself and spreads through the surrounding subcutaneous tissue.

Most of the time cellulitis is caused by streptococcal and staphylococcal bacteria. These bacteria can be highly virulent, meaning that it can withstand the immune system and cause extensive damage. However, antibiotics are able to treat and eradicate these infections.

The greater concern is when drug-resistant bacteria like methicillin-resistant Staphylococcus aureus (MRSA) enter the body and cause an infection like cellulitis. It may require a cocktail of drugs to eradicate this infection. Drug-resistant bacteria are becoming a gloal problem in all types of diseases, not just cellulitis.

Any person of any age can develop cellulitis if the bacteria reach the subcutaneous tissue. However, certain people are at a greater risk. The elderly, people with immune-suppressing diseases like poorly controlled diabetes and HIV or AIDS, as well as people using immune-suppressing drugs like cancer drugs (chemotherapy) are at a greater risk of developing cellulitis and experiencing complications like septicemia.

Read more on how to prevent cellulitis.

How To Spot Cellulitis

Cellulitis should be suspected after an injury that causes a break in the skin where the symptoms mentioned below develops. It may also start as a superficial infection of the skin and then spread to deeper layers. Cellulitis should always be treated by a medical professional. If it is evident that the infection is spreading and there is a high fever then it must be considered a medical emergency. Immediate medical attention is necessary.

Skin Injury

A cut or some other break in the skin is usually visible at the site where the cellulitis starts. This may occur in various different ways, a deep insect bite, a piercing with a sharp object or some similar lesion. Sometimes this break in the skin is not clearly visible – it may be very small but bacteria are still able to enter the deeper tissue. Cellulitis can occur as a complication of more superficial skin diseases, such as fungal infections, and these rashes may also be visible at the site where the cellulitis begins.

Red Rash, Spots, Blisters

A red rash is present that usually starts at the site of inoculation (where the bacteria enter the tissue under the skin). As the infection spreads the redness also spreads. In the legs it may spread upwards to the torso or downwards to the feet. The redness is a sign of inflammation. Red spots may also be present on or around the rash. Sometimes small blisters form, especially at the site where the bacteria enter the body. These red spots and blisters may arise before the other symptoms, especially if there is an infection of the superificial layers (impetigo or erysipelas).

Swelling and Heat

Accompanying the red rash is swelling and heat which are two other features of inflammation. The affected area may appear slightly elevated and feel spongy, indicating fluid accumulation in the underlying tissue. Heat may also be detected at the site of rash compared to surrounding unaffected tissue. The extent of the swelling and heat usually correlates with the degree of redness and pain or tenderness. Inflammation is the body’s response to injury and causes an increase in blood flow and immune activity at the affected site.

Pain and Tenderness

Tenderness is present from the early stages and may precede the other symptoms. It gradually worsens as the infection progresses. The tenderness is usually at the point of infection and surrounding tissue. It extends with the the spread of the infection. Pain may eventually arise and can extend beyond the affected site. Both tenderness and pain may also be a result of the initial injury which allowed for the bacteria to enter due to the break in the skin.

Fever and Chills

Fever is another common sign of cellulitis but may not be present in the early stages. It is more likely to occur as the infection worsens and spreads. There may also be chills (shivering) associated a feeling of coldness that are common in fevers. One of the concerns with a high fever is that it may be a sign of the infection having entered the bloodstream and possibly spreading throughout the body (septicemia).


Malaise is a feeling of being unwell which usually occurs in later stages of cellulitis. Sometimes it may arise early in the infection, even when other symptoms have not become evident. It is sometimes mistaken for a cold or flu in these early stages. Malaise tends to worsen as teh infection progresses and peaks when complications like septicemia arises from cellulitis.

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