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What you need to know about cellulitis

What is Cellulitis?

Cellulitis is a deep dermis bacterial skin infection involving the skin’s subcutaneous tissue. The lesion doesn’t have sharp edges, but the affected area is highly tender and red, resulting in swollen skin. A group of bacterial organisms is responsible for this condition, higher in individuals with a weakened immune system. [1]

Cellulitis can present itself as a rash and/or nodules on the skin, which suggest inflammation of the body’s cells due to a bacterial infection. Individuals with cellulitis have reported it appearing on various parts of the skin. Cellulitis affects more than 15 million people in the United States. Because of its increasing prevalence, knowing what causes this disease and how to prevent it is crucial, as immediate treatment can significantly improve the prognosis of the disease.


Our skin has a number organisms lying on top of it, which cannot gain entry inside the skin because of its tough fibres which work to stop their penetration. All the normal skin flora enter the body’s deeper tissues when this barrier gets breached. These organisms multiply inside our bodies thanks to the optimal environment provided to them; this causes many causing problems.

Many microorganisms are present worldwide, and the ones that cause Cellulitis belong to the gram-positive cocci group resulting in bacterial infection.

That group of organisms includes the group A beta-hemolytic Streptococcus pyogenes. Cellulitis is an acute bacterial infection caused due to pathogens reaching the lymphatic systems and the subcutaneous tissue through a break in the skin.

Besides skin trauma, people bitten by animals also undergo Cellulitis. The organisms responsible in such cases are Gram-negative bacteria. Pasteurella, Capnocytophaga, Vibrio, and Aeromonas are all responsible for causing inflammation of the affected skin in such cases.

Older people, diabetics and individuals with a weakened immune system are prone to Cellulitis. They end up developing cellulitis due to their immunocompromised state. [2]


Cellulitis, a common bacterial skin infection, occurs when Staphylococcus aureus or strep bacteria enter the skin through any break. That results in the entry of the bacteria releasing several chemicals to invade the affected area, spread rapidly and reproduce. The body activates the process of inflammation to get rid of the bacteria and nullify their effects on the body by reaching the deeper layers.

The process of inflammation begins with increased blood flow to the area that has been affected. Next, the capillaries of that area become leaky, and the neutrophils enter the tissue affected by the bacteria. More cell mediators, such as cytokines, also reach the site of infection to control the spread of the bacteria and its harmful toxins.

These cells produce antimicrobial proteins to destroy the organism. The most common bacteria that cause Cellulitis Group A Streptococci. These bacterial organisms release exotoxins, making it more difficult for the body to eradicate them from the body. [3]

Symptoms of cellulitis

Symptoms of Cellulitis are the same as those seen in any body’s inflammatory process. It can happen anywhere in the body, but it is more common on the hands, lower legs and feet; other symptoms have been mentioned.

Following symptoms seen in people affected by this disease are as follows;

  • Red and warm skin
  • Tender on touch
  • Swollen skin due to the blood plasma pooling in the area.
  • Fever accompanied by chills
  • Ulcers and spots on the skin
  • Presence of blisters
  • Skin discoloration
  • Skin rash and cellulitis itch
  • Dimpling and pitting of the skin

Early treatment of active infection can help stop the disease from turning into a skin abscess or causing sepsis, where the organism gains entry into the blood. That typically affects the deeper tissues of the body and causes Necrotizing Fasciitis. [4]

Risk factors

Cellulitis is a condition that can be prevented if cared for during routine and otherwise. The risk of developing cellulitis varies considerably. Following is a list of all the factors that increase the likelihood of getting Cellulitis;

  • Break in the skin

Anything that causes a skin barrier breaks is an invitation for germs and bacteria to enter. Therefore, in any skin wound, injury or minor cut, it is essential to use antiseptics over the wounds to kill the bacteria immediately. Individuals who suffer from atopic dermatitis have cracks in their skin, increasing the risk of cellulitis.

  • Lymphedema

Individuals with lymphedema develop cellulitis as the lymph nodes cannot drain the excess fluid back; this causes fluid pooling in one place, increasing the risk of cellulitis and other bacterial diseases as puncture wounds are easily formed due to skin friability.

  • Surgical incisions

Those undergoing surgery can also be prone to a Cellulitis infection if aseptic techniques are used. In some cases, such as peritonitis, there is contamination with the bodily fluids which can harvest bacteria. Moreover, individuals with an open wound are very likely to acquire a deep-layer infection. However, the prophylaxis cover of antibiotics can limit that before the surgical procedure.

  • Insect and animal bites

As mentioned earlier, many insects or animal bites can also irritate the skin. That is because the skin gets punctured and invites bacteria inside the dermis and subcutaneous tissue. Cellulitis diagnosed in such individuals requires a deeper evaluation to ensure the bite’s effects are neutralised.

  • Chronic skin conditions

Some skin conditions, if left untreated, can cause complications. For example, individuals with fissures in their toes, tenia pedis, or athlete’s foot (fungal infections) are more likely to get a Cellulitis infection in those regions. That is due to a superimposed condition and requires antibiotics at the earliest.

  • Drug use injections

Drug addicts are more likely to suffer from Cellulitis due to injecting drugs and the unsanitary use of syringes. These cause the skin to get ulcerated and develop various diseases on top of Cellulitis.

  • Obesity

According to research, it has been seen that people who are underweight or obese are at a higher risk of developing cellulitis than the ones who are not.

  • Venous insufficiency

People with coronary artery bypass or diseases resulting in poor circulation develop cellulitis. A blood clot can be formed and result in further life-threatening complications. [5]


To diagnose cellulitis, doctors take a history, notice symptoms of cellulitis, and then perform a physical examination to check the signs. The affected area presents with a patch of red skin that does not have a proper margin or a border. The skin swelling and tenderness become obvious on palpation. Moreover, symptoms such as fever, fatigue and generalised weakness are all signs that point towards cellulitis.

It is essential to gather pointers from the history, such as any recent travel to a place, history of intravenous drug use, or trauma to the skin. Moreover, insect and animal bites are also essential clues towards diagnosing Cellulitis.

The history also includes a detailed past medical history that helps evaluate if the person has any chronic medical conditions such as; diabetes mellitus, lymphedema, athlete’s foot, or any vascular disease that can result in poor circulation. This also clues whether the individual has a weak immune system.

Cellulitis is primarily present on the lower extremities, so the space between the toes and the fingers is adequately inspected. Signs of blisters and pitting of skin all point towards Cellulitis.

Blood samples were drawn to confirm the diagnosis are not that important, however. However, blood pictures can show an increased number of neutrophils and white blood cells, which can aid in diagnosing.

A diagram of cellulitis

Blood cultures are necessary for individuals who develop systemic complications and sepsis. [6]

Cellulitis Treatment

The treatment of Cellulitis depends on the severity of the disease, whereas the prognosis depends on the person’s immune system. Individuals with mild cellulitis require a different treatment plan than those with moderate to severe Cellulitis and need much more aggressive forms of therapy.

  • Mild Cellulitis

Individuals who only present with skin discoloration and no systemic effects are considered to have a mild form of cellulitis. They need antibiotics targeting the staph species and proper oral antibiotic therapy to overcome their disease.  Antibiotic ointment and oral antibiotics are given for a minimum of five days. Compression of the affected area to reduce swelling also helps alleviate the symptoms.

  • Moderate Cellulitis

Individuals have moderate cellulitis if they have purulent discharge, abscess formation, or a history of intravenous drug use. These develop a more severe infection and are likely to have Methicillin-resistant Staphylococcus aureus. These individuals need broad-spectrum antibiotics to recover completely.

A longer duration of antibiotic therapy is considered in individuals who do not respond to antibiotics within 48 hours.

  • Severe Cellulitis

Severe cases of cellulitis are when systemic complications arise. The infection spreads by crossing the blood barrier, and organisms start circulating in the blood, causing sepsis. Furthermore, the affected tissue of the individual also undergoes necrosis. Individuals with progressive oedema, recurrent cellulitis, and such require hospital admission and need to get surgical debridement done.

Untreated cellulitis can lead to permanent swelling and necrotising fasciitis, a life-threatening complication of this disease. Compression stockings can be used to reduce swelling.

Any individual who starts exhibiting systemic signs needs to get their blood culture done to get their cellulitis treated. [7]

Is cellulitis contagious?

Some wonder whether cellulitis can travel from person to person just by sharing foods or drinks. No data has been recorded that suggests this skin condition gets transmitted from one person to another through such means.

Serious complications

Cellulitis usually does not require aggressive forms to treat cellulitis. It is taken care of at the early stages only. Bacterial infections can be taken care of with early diagnosis and treatment.

The patient’s prognosis depends on the degree of severity of the progress of the disease. If the organisms reach the bloodstream, it leads to bacteremia and sepsis, and it is essential to control it before such symptoms begin.

Some of the complications that arise due to untreated cellulitis are as follows;

  • Endocarditis
  • Osteomyelitis
  • Necrotizing Fasciitis
  • SIRS
  • Suppurative arthritis [8] [9]

To prevent cellulitis and such life-threatening complications, treatment must be done as soon as the symptoms appear.


  1. Brown BD, Watson KL. Cellulitis. InStatPearls [Internet] 2021 Aug 11. StatPearls Publishing.
  2. Liu, C., Bayer, A., Cosgrove, S.E., Daum, R.S., Fridkin, S.K., Gorwitz, R.J., Kaplan, S.L., Karchmer, A.W., Levine, D.P., Murray, B.E. and Rybak, M.J., 2011. Clinical practice guidelines by the Infectious Diseases Society of America for treating methicillin-resistant Staphylococcus aureus infections in adults and children. Clinical infectious diseases, 52(3), pp.e18-e55.
  3. Kranendonk DR, Lavrijsen AP, Prins JM, Wiersinga WJ. Cellulitis: current insights into pathophysiology and clinical management. Neth J Med. 2017 Nov 1;75(9):366-78.
  4. Baxter H, McGregor F. Understanding and managing Cellulitis. Nursing Standard (through 2013). 2001 Jul 18;15(44):50.
  5. Chlebicki MP, Oh, CC. Recurrent Cellulitis: risk factors, aetiology, pathogenesis and treatment. Current infectious disease reports. 2014 Sep;16(9):1-8.
  6. Phoenix G, Das S, Joshi M. Diagnosis and management of cellulitis. BMJ. 2012 Aug 7;345.
  7. Vijayalakshmi B, Ganapathy D. Medical management of Cellulitis. Research Journal of Pharmacy and Technology. 2016;9(11):2067-70.
  8. Carratala J, Roson B, Fernandez-Sabe N, Shaw E, Del Rio O, Rivera A, Gudiol F. Factors associated with complications and mortality in adult patients hospitalised for infectious Cellulitis. European Journal of Clinical Microbiology and Infectious Diseases. 2003 Mar;22(3):151-7.
  9. Centres for Disease Control and Prevention. (2022, June 27). Cellulitis. Centres for Disease Control and Prevention. Retrieved October 24, 2022, from https://www.cdc.gov/.html

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