The Heat Is On: Understanding Thermal Burns

By Sarabeth Lowe, MPH

Ms. Lowe is a Communication Specialist at the University of Delaware Disaster Research Center.

Burns are likely one of the most common injuries worldwide.^1–8 Burns go more than just skin deep; they are complex, dynamic injuries that activate numerous responses in the body; all have the potential to be physically and psychologically devastating no matter the size or severity.^4,5,9,10 According to the World Health Organization, an estimated 180,000 deaths every year are caused by burns, and nonfatal burns are the leading cause of morbidity (ill health) worldwide.³ Roughly 600,000 people in the United States suffer from a burn injury each year, though estimates vary.¹¹ 

A burn is a traumatic injury to the skin (and sometimes the underlying tissue) caused by contact with extreme temperatures, chemicals, radiation, or electricity.^1,4,12–15 These causes have helped researchers develop 5 categories for burns: chemical, electrical, radiation, friction, and thermal.^2,4,14–18 This article will focus on thermal burns, which occur upon contact with extreme temperatures.^14,17,19,20

An Injury of Extremes

Thermal burns can be caused by both hot and cold temperatures. Cold-induced injuries, like frostbite and ice burn, can also cause skin and tissue damage with lasting consequences. Research shows that the degree of tissue damage can be much more significant with frostbite because extended exposure to freezing temperatures can lead to ice crystals forming in the tissues. Cessation or reduced blood flow can lead to permanent damage to skin, muscles, and even bones.^4,21–24 This lack of circulation is also why amputation is more common with cold-induced burns; dead tissue cannot be revived. Like heat-induced injuries, cold burns can cause irreversible, long-term, and devastating injuries.

Types of Thermal Burns

Thermal burns are categorized into 4 groups based on the source of injury.

Contact. This kind of burn happens when your skin comes into contact with an extremely hot surface, such as a stove, car engine, or hearth. In many cases, these burns aren’t deep, but depending on the temperature and length of exposure, the heat can transfer quickly and damage the outer and sometimes deeper layers of the skin.^1,25 These burns can happen in seconds and are likely the most common type of thermal burn.

Flame. Flame burns happen when skin comes into direct contact with fire. They often occur in house fires, car accidents, during firework displays, when clothing catches fire, or at campfires. These burns can be severe because they affect deeper layers of tissue, larger areas of the body, and may damage the airway or lungs if smoke or heat is inhaled.^1,26

Flash. Sometimes grouped together with flame burns, flash burns are caused by short, intense, usually indirect exposure to flame or a burning gas or vapor.^1,16,27,28 They can be caused by flash fires, steam, or a minor combustion event (eg, when food “pops” when cooking on a grill). They can cause minor-to-major injury depending on the explosion’s strength. 

Scald. A scald burn is caused by a hot liquid, such as boiling water, grease splashes, steam, or a beverage, coming into contact with the skin.^1,29 These burns can happen in seconds, affect large swathes of skin, and cause long-term damage if not treated properly in a timely manner.

Some researchers also consider electric burns, which are caused by contact with an electrical current or a strike through the body, thermal burns. These currents create heat in the body that can cause extreme internal and external damage.^1,30 Though the skin damage may seem minor or invisible, electric burns can be life-threatening because they can affect deeper tissues, muscles, nerves, and the heart.

Anatomy of the Skin

Since thermal burns largely injure the skin, it is important to understand the skin’s composition. Skin is the body’s central sensory organ and first line of defense against infection or physical damage.^4,31–34 Even at the skin’s thickest points (eg, soles, palms), it is still only a few millimeters thick.^.32 The skin has 3 layers.^{4,12,14,31,32,35} The outer, thinnest layer is called the epidermis. It continuously creates new cells in its lower layer to replace cells that are naturally shed from the skin’s surface. Underneath the epidermis is the dermis, the middle and thickest layer. It contains collagen and elastin, which support your skin’s overall structure; connective tissues; nerve endings; hair follicles; and sweat and oil glands.^31,35,36 The innermost layer is the hypodermis. This fatty, subcutaneous layer is made up of connective tissue that cushions your muscles and bones.^{4,12,31,32,35}

Burn Classification

Healthcare providers consider several factors when evaluating a burn and use 2 specific variables to determine treatment: depth and size, measured as a percentage of the total body surface area (TBSA) affected.^{1,2,4,5,13,14,18,37–39} For decades, the degree system was the default mechanism for evaluating burns. However, this concept has slowly been phased out in the literature for determining morbidity and mortality,^{1,2,4,5,12,14,18,20,33,34} since it does not account for age, location on the body, pre- or co-existing health conditions, and—perhaps most importantly—inhalation injury from smoke or other fumes. For example, a minor 3-inch burn on the face of an adult may be easily managed at home, but one on an infant could have devastating consequences without treatment from a burn center.

The current convention for classifying burns is based on how deeply the injury penetrates the layers of the skin. The American Burn Association (ABA) uses 4 categories to determine burn depth.^11,18,40

Superficial. These burns only damage the epidermis. The affected area becomes red, sore, and might peel, but not blister. These burns are minor and can be treated at home. They usually heal within 5 days and do not scar. An example of this injury is a mild or moderate sunburn.^11,18,40

Superficial partial-thickness. These burns reach in the dermis and may cause more significant pain, blisters, and swelling. Also considered minor burns, these injuries usually heal within 2 weeks and can be treated at home, though professional medical intervention may be needed depending on the size and location on the body.^11,18,40 

Deep partial-thickness. These burns involve damage to all 3 layers of the skin and may penetrate deeply enough to affect muscle, fat, or bone. The skin may appear white, black, or leathery and feel numb or painless because the nerve endings are damaged. These are considered major burns and require medical intervention, such as skin grafts.^11,18,40 

Full-thickness. Also known as fourth-degree burns, these burns destroy all 3 layers of skin and cause substantial damage to subcutaneous tissues and bone. The term “fourth-degree burn” is not often found in the literature or used in diagnoses because they are often fatal.^1,4,41 Also considered a major burn, these injuries always require emergency care and medical intervention.^11,18,40

Your skin can be damaged in many ways, but the way our body responds to burns is particularly unique. Notably, burns are dynamic wounds. Most will heal endogenously, meaning the body can repair and regenerate the skin on its own.^{1,2,4,12,16,41–43} With burns, this means that the cells produced in the lower layer of the epidermis rise to the skin’s surface and start the healing process. The body might be able to do this on its own or require some help from a specialized burn care professional who can apply biomaterials that mobilize the body’s natural healing abilities or replace the injured tissue.^42,43

The depth of these injuries can change over time, which is a process known as conversion.^1,33,43,44 A burn that was initially diagnosed as a superficial partial-thickness burn can turn into a deep partial-thickness injury after a few days as the damage penetrates the skin more deeply. This means that you can have more than 1 type of burn injury at a time. Not much is known about this phenomenon, but conversion seems to become more likely with desiccation of the wound bed (ie, when the skin becomes dehydrated and dries out) and infection.

Seeking Treatment

The 2 most important factors affecting burn mortality, morbidity, and recovery are a person’s age and the size of the injury.^{1,2,4,14,16,33,34,39,45,46} The ABA recommends that patients with a burn who meet any of the following criteria be treated at a specialized burn center:^{11,39,40,47–49}

• All pediatric patients (≤14 years or weighing <30 kg)
• Full-thickness burns
• Partial-thickness burns that cover ≥10% of the TBSA
• Deep partial- or full-thickness burns involving the face, hands, genitalia, feet, perineum, or joints
• Concurrent burns and other comorbidities, concomitant traumatic injuries, or poorly controlled pain
• Suspected inhalation injury
• Most minor thermal burns can be fully treated at home. Proper and timely care is important for more than just managing pain and promoting faster healing; it also helps prevent infection. Burn wounds are particularly vulnerable to infection because your skin is your primary defense against germs, bacteria, and other potentially dangerous microorganisms from entering the body.^{1,4,20,33,34,39,43,46,49–53} In fact, post-injury infection—not shock or organ damage—is likely the leading cause of burn-related death and morbidity.^4,52–55 

Treating Minor Burns

The ABA recommends the following 4 steps for treating minor burns at home:^{11,18,25,26,29,39,47–49}

Cooling and cleansing. Calmly remove yourself from the heated area, stopping the process or turning off the burning source if you can. Cool the burn immediately with running water—avoid cool, cold, or icy water—for 10 to 20 minutes. Unless it is stuck to the skin, remove any clothing or jewelry from the affected area. Do not pop any blisters, which protect the skin as it heals.

Topical relief and protection. Cover the injured area with a clean, dry, breathable, nonstick dressing while it heals. Applying soothing gels, like aloe vera, or unscented moisturizers can help keep skin hydrated, which can reduce itching and discomfort.^{38,47,56–58} This process can be repeated up to 3 times per day. Never apply ointments, such as petroleum jelly, as immediate burn treatment, as this can trap heat.^56,58–60

Infection prevention. Keep the burn clean and dry, and monitor the area for signs of infection, such as increased redness and pain, swelling, and drainage.^{1,2,4,12,39,47,49,53,56} Many topical over-the-counter treatments for burns are antimicrobial. Gently clean the affected area with mild soap and water before applying it to your skin. If you suspect the burn is infected, your doctor might prescribe an oral antibiotic. Notably, burns are particularly vulnerable to tetanus.^60,61 Seek care immediately if you develop a fever, experience muscle stiffness, or if it has been over 5 years since your last tetanus booster shot.

Pain management. Many burn relief treatments are multipronged and can help with pain management in addition to preventing infection and itching.^{4,11,17,25,34,47,56,58,62} However, avoid ones that contain lidocaine and menthol, as these should not be used on open wounds or severe burns. Instead, use over-the-counter pain medicine, such as acetaminophen, ibuprofen, naproxen, or aspirin, to reduce pain and complement other treatments.^11,60

No burn wound is the same, and treatment strategies and recovery time may vary depending on the severity of the injury. However, most minor burns heal within 3 weeks and are unlikely to leave a permanent scar.^{1,11,20,37,51,63} Always consult your doctor for advice if you’re unsure of the burn’s severity, the affected area is larger than your hand, or your condition worsens.

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