Cellulitis vs. Impetigo: Definitions, Causes, and Effective Management Strategies

Cellulitis and impetigo are both common bacterial skin infections that present a significant burden to global health. Despite their prevalence, these conditions are often misunderstood by the general public.

Cellulitis, a potentially serious infection that can spread to the lymph nodes and bloodstream, leads to over 650,000 hospital admissions annually in the US alone. The economic impact is profound, with an estimated 14.5 million cases of cellulitis each year, resulting in $3.7 billion in ambulatory care costs. The severity of cellulitis and its capability to spread rapidly highlights the importance of early diagnosis and treatment. On the other hand, impetigo, primarily affecting children, is highly contagious and presents differently, indicating the necessity of distinguishing between these infections for effective management and prevention.

In this article, you will learn about the definitions, causes, risks, symptoms, diagnosis, treatment, and prevention of cellulitis and impetigo. Understanding these aspects is crucial for early recognition and management, which can significantly improve patient outcomes and reduce the healthcare burden of these skin infections.​

1. Definition

Cellulitis and impetigo are common bacterial skin infections, yet they manifest and affect individuals differently.

Cellulitis

Source: NHS

Cellulitis is a deep bacterial infection of the skin, primarily caused by streptococcus and staphylococcus bacteria. It presents as a swollen, red area of skin that is hot and painful to touch and often spreads rapidly. While it can occur on any body part, the lower legs are the most common site.

Cellulitis can spread to the lymph nodes and bloodstream, posing serious health risks if not treated promptly. Factors that facilitate bacterial entry leading to cellulitis include:

• Skin breaks from wounds
• Ulcers
• Dermatitis

The condition affects individuals of all ages but has a significant incidence and hospital admission rate, notably in the US, where it contributes significantly to healthcare costs. Complications of cellulitis may include abscess formation and severe systemic infections like sepsis if not correctly managed​.

Impetigo

Source: CDC

Impetigo is a highly contagious surface skin infection that primarily affects infants and young children, though it can occur in individuals of any age. Caused by Staphylococcus aureus and sometimes by Streptococcus pyogenes, impetigo is characterized by red sores that pop, ooze for a few days, and then form a honey-colored crust.

It usually appears around the nose and mouth but can spread to other body parts through contact with an infected person or objects. Impetigo can present in nonbullous, bullous, and ecthyma forms, with nonbullous being the most common.

This condition is especially prevalent in warm climates and crowded living conditions. Without treatment, impetigo generally resolves within three weeks, but complications can include cellulitis and kidney problems. Impetigo had a global effect, with an estimated 140 million people affected in 2010, highlighting its prevalence and the importance of effective management strategies to prevent spread and complications​.

2. Cause and Risk Factors

Both cellulitis and impetigo arise from bacterial infections, but the conditions differ in how and why they develop in individuals.

Cellulitis

The primary culprits behind cellulitis are bacteria, with Streptococcus and Staphylococcus aureus being the most common. These bacteria can easily invade the skin through cuts, cracks, insect bites, surgical incisions, or wounds, leading to infection.

There are several factors that increase an individual's susceptibility to developing cellulitis:

• Skin Breaks: Any damage to the skin's integrity, including cuts, wounds, or ulcers, significantly increases the risk as it provides an entry point for bacteria.
• Weak Immune System: Individuals with weakened immune systems, due to conditions like diabetes, HIV/AIDS, or through the use of certain medications, are more susceptible to cellulitis.
• Skin Conditions: Eczema, athlete's foot, and other skin issues that cause breaks in the skin surface can serve as entry points for bacteria, raising the risk of cellulitis.
• Previous Cellulitis: Those who have had cellulitis before are at a higher risk of recurrence.
• Lymphedema: Swelling of limbs, which can compromise the skin and make it easier for bacteria to invade, is also a risk factor.

Environmental factors, such as exposure to water or living in crowded conditions, can also increase the risk of cellulitis, as they may facilitate the entry of bacteria through minor skin abrasions.

Impetigo

Impetigo is mainly caused by Staphylococcus aureus and Streptococcus pyogenes. It starts with bacteria invading the skin, typically through small cuts, insect bites, or any form of break in the skin. It can also develop in completely intact skin.

Several factors increase an individual's susceptibility to developing impetigo:

• Age: It primarily affects children between the ages of 2 and 5 but can occur in people of all ages.
• Close Contact: Impetigo is highly contagious, so it spreads easily in schools, childcare environments, and households.
• Warm, Humid Weather: These conditions are conducive to the spread of impetigo.
• Broken Skin: Just like cellulitis, breaks in the skin from injuries or skin conditions provide a pathway for bacteria.
• Crowded Conditions: Living in crowded environments can facilitate the spread of impetigo.
• Poor Hygiene: Not cleaning the skin properly after injuries can increase the risk of impetigo.

Impetigo is notable for its high contagion level, with the infection spreading through direct contact with sores or even items touched by the infected person, such as towels, bed linens, or clothing. Preventive measures, such as good hygiene practices and minimizing close contact with infected individuals, are crucial to control its spread.

3. Symptoms

The clinical manifestations of cellulitis and impetigo significantly differ, not just in appearance but also in how they affect individuals. Recognizing these symptoms is crucial for timely diagnosis and treatment.

Cellulitis

Cellulitis typically presents as a red, swollen, and tender area of skin that may rapidly spread. It often feels warm or hot to the touch. The infection can occur anywhere on the body but is most commonly found on the lower legs. Key symptoms include:

• Redness and swelling
• Pain and tenderness in the affected area
• Warmth over the area of redness
• Fever and chills in some cases, indicating a more severe infection
• Blisters or a red streaking from the infection site may also be present

The skin may also feel tight or stretched, and individuals with cellulitis might experience an overall feeling of malaise. In severe cases, symptoms can escalate to dizziness, lethargy, and a high fever, signaling the spread of infection to the bloodstream.

Impetigo

Impetigo, highly contagious and primarily affecting children, shows up distinctly from cellulitis. It begins as red sores or blisters that rupture, ooze, and then form a yellowish-brown crust. The sores are not typically painful but can be itchy. Impetigo commonly affects the face, especially around the nose and mouth, as well as the hands and feet. The two main types, nonbullous and bullous impetigo, exhibit slightly different symptoms:

• Nonbullous Impetigo: Characterized by the appearance of red sores that quickly rupture and ooze for a few days, forming a honey-colored crust. It's the more common form and can spread to other body parts.
• Bullous Impetigo: This form presents larger blisters filled with a clear fluid that becomes cloudy. These blisters can be more widespread and often leave a red mark on the skin after breaking but heal without scarring.

Ecthyma, a more serious form of impetigo that penetrates deeper into the dermis, can cause painful fluid- or pus-filled sores that turn into deep ulcers, potentially leading to scars.

4. Diagnosis

Given their distinct characteristics and the layers of skin they affect, diagnosing cellulitis and impetigo involves different clinical approaches.

Cellulitis

Diagnosing cellulitis primarily involves a physical examination. Healthcare providers look for signs of skin infection, such as redness, warmth, swelling, and tenderness. Since cellulitis can spread quickly and affect other body parts, identifying systemic symptoms like fever is crucial. The following are the key diagnostic methods used:

• Physical Examination: The doctor assesses the affected skin area's appearance and symptoms. They may also check for signs of insect bites, cuts, or other wounds that could have served as entry points for bacteria.
• Blood Tests: In some cases, especially if the patient has a fever or shows signs of a systemic infection, blood tests may be performed to check for bacteria in the blood.
• Imaging Tests: Rarely, if the doctor suspects that the infection has spread deeper, imaging tests like an ultrasound or MRI might be ordered to check for abscesses or deeper tissue involvement.

Prompt diagnosis is essential for starting the appropriate treatment to prevent the spread of infection.

Impetigo

Impetigo is usually diagnosed based on the appearance of the skin lesions. The distinctive sores and blisters, especially when they crust over, are often enough for healthcare providers to identify the infection. Alongside visual inspection, healthcare providers employ additional diagnostic methods:

• Visual Inspection: The key to diagnosing impetigo is recognizing the classic symptoms, such as red sores that burst and develop a honey-colored crust. The sores’ location around the nose and mouth or on the hands and feet is also a clue.
• Culture and Sensitivity Tests: If the diagnosis is uncertain or if the impetigo doesn't respond to initial treatment, a culture of the bacteria from the sores may be taken. This can help identify the bacteria causing the infection and determine the most effective antibiotics for treatment.
• Differential Diagnosis: It's crucial to differentiate impetigo from other skin conditions like eczema or herpes simplex virus infection, which can sometimes mimic impetigo's symptoms.

5. Treatment Options

Cellulitis and impetigo have different treatments, reflecting their nature and severity. Effective treatment addresses the infection and aims to prevent recurrence and complications.

Cellulitis

When it comes to managing cellulitis, the primary treatment revolves around antibiotics, which can be administered orally or intravenously, depending on the severity of the infection. Alongside antibiotics, several supportive measures are employed:

• Antibiotics: Oral antibiotics for cellulitis are usually effective for mild to moderate cases of cellulitis. The type of antibiotic prescribed depends on the bacteria suspected of causing the infection and the patient's medical history. Common antibiotics include cephalexin and clindamycin. For more severe cases, especially those showing signs of spreading or in patients with high fever or significant lymph node involvement, intravenous antibiotics may be required.
• Pain Management: Over-the-counter pain relievers may be recommended to help reduce discomfort.
• Rest and Elevation: Patients are advised to rest and keep the infected area elevated to reduce swelling and promote healing.
• Monitoring: Follow-up is crucial to ensure the infection is responding to treatment. If symptoms worsen or do not start to improve within a few days, a healthcare provider may need to adjust the treatment plan.

Impetigo

Similarly, for impetigo, treatment aims to clear the infection, heal the skin, and prevent its spread. Treatment methods include:

• Topical Antibiotics: For localized impetigo, topical antibiotics like mupirocin or fusidic acid are often effective and are applied directly to the sores.
• Oral Antibiotics: When impetigo is widespread or does not respond to topical treatment, oral antibiotics may be necessary. The choice of antibiotic depends on the bacteria involved and the infection's extent. Penicillin or amoxicillin is commonly prescribed.
• Hygiene Measures: Keeping the affected area clean and covered helps prevent the spread of impetigo. It's also important for the patient to wash their hands frequently and avoid scratching the sores.
• Isolation: Children with impetigo should stay home from school or daycare until they're no longer contagious, usually 24 hours after beginning antibiotic treatment.

6. Prevention

Preventing cellulitis and impetigo is crucial for reducing their incidence, especially given their infectious nature and potential for complications. Here are strategies for preventing both conditions:

Cellulitis

Since cellulitis often enters through breaks in the skin, the following measures can help reduce the risk of infection:

• Wound Care: Clean all cuts, abrasions, or breaks in the skin promptly and apply a protective cream or ointment. Cover wounds with a sterile bandage.
• Hygiene: Regularly wash your hands and keep your skin clean to reduce the risk of introducing bacteria to wounds.
• Moisturize Your Skin: Keeping skin moisturized can prevent cracking and peeling, reducing entry points for bacteria.
• Protective Gear: Use appropriate protective gear during activities that might injure the skin, such as gardening or sports.
• Manage Chronic Conditions: Conditions like diabetes or vascular disease can increase the risk of cellulitis. Effectively managing these conditions can reduce your risk.

Impetigo

Preventing impetigo focuses on hygiene and avoiding the spread of the infection:

• Good Hygiene: Wash your hands regularly and bathe with soap and water, especially after touching infected sores or items like towels or bed linens used by someone with impetigo.
• Do Not Share Personal Items: To reduce the risk of spreading bacteria, avoid sharing towels, clothes, bed linens, and sports equipment.
• Short Nails: Keep fingernails short to prevent the collection of bacteria under the nails and reduce the chance of breaking the skin by scratching.
• Avoid Touching Sores: If you or your child has impetigo, avoid touching or scratching the sores to prevent the bacteria from spreading to other parts of the body or to other people.
• Isolate Contagious Individuals: People with impetigo should be kept home from school or work until they're no longer contagious—usually for at least 24 hours after starting antibiotic treatment.

Final Words

Despite their differences, cellulitis and impetigo highlight the critical balance between bacteria and the skin's role as a barrier to infection. Advances in medical treatments and ongoing research into the mechanisms of bacterial skin infections continue to improve outcomes for individuals affected by these conditions.

Ultimately, education and awareness about these infections can empower individuals to take proactive steps in prevention, early detection, and treatment, contributing to better health and well-being.

Frequently Asked Questions

Are cellulitis and impetigo contagious?

Cellulitis isn’t usually contagious. However, impetigo is highly contagious and can be spread through direct contact with an infected person or their belongings.

What is the main cause of cellulitis, and can poor hygiene cause it?

Cellulitis is caused by bacteria entering through a break in the skin. While often related to wounds or bites, poor hygiene can also contribute to its development.

What are the complications associated with cellulitis?

Though uncommon, complications from cellulitis can include serious infections like bacteremia, suppurative arthritis, osteomyelitis, endocarditis, and thrombophlebitis​​.

How can I reduce my risk of developing cellulitis?

Preventive measures include washing hands often, cleaning and caring for wounds, and avoiding hot tubs, swimming pools, or natural bodies of water with open wounds. Diabetics should monitor their feet for infections.

What differentiates erysipelas, cellulitis, and impetigo?

Erysipelas affects the upper layers of the skin with clear borders, cellulitis involves deeper layers with no clear borders, and impetigo is a surface infection characterized by crusty sores.

What is periorbital cellulitis and its treatment?

Periorbital cellulitis, also known as preseptal cellulitis, is an infection of the eyelid and surrounding areas requiring oral antibiotic treatment. Orbital cellulitis occurs when the infection penetrates into the muscles and fat surrounding the eye. This is a much more serious type of infection that requires IV antibiotics and close follow-up with an ophthalmologist.