A burn is tissue damage caused by heat, chemicals, electricity, or radiation that destroys proteins in your skin cells. The severity depends on how deep the damage reaches and how much of your body is affected. Burns range from minor, superficial injuries that heal on their own in a few days to life-threatening emergencies that require specialized hospital care.
How Burns Damage Your Skin
Your skin is made of layers. The outermost layer, the epidermis, acts as a barrier against bacteria and water loss. Below that sits the dermis, which contains nerve endings, blood vessels, sweat glands, and hair follicles. Beneath both is a layer of subcutaneous fat that insulates and cushions deeper structures like muscle and bone.
When a heat source contacts your skin, the proteins in your cells begin to break apart, a process called denaturation. The cells die, and the surrounding tissue launches an inflammatory response: blood vessels dilate, fluid leaks into the damaged area, and immune cells rush in. This is why even a mild burn turns red and swells. In deeper burns, the damage extends far enough to destroy the blood supply to the skin itself, killing the tissue outright.
Types of Burns by Source
Most people think of burns as heat injuries, but several different energy sources can cause them.
- Thermal burns come from flames, hot liquids, steam, or contact with hot surfaces. These are the most common type.
- Chemical burns result from contact with acids, alkalis (like lye or ammonia), or industrial chemicals. Acids tend to cause localized damage by hardening the tissue at the surface. Alkalis are often more dangerous because they dissolve fat and penetrate deeper into the skin, causing damage that continues to spread.
- Electrical burns occur when electrical current passes through the body. The current drives water into cell membranes, causing them to rupture. Bone has the highest resistance to electricity, so it heats up the most and can burn surrounding muscle from the inside out. This means electrical burns are often far worse internally than they appear on the skin’s surface. Electrical arcs can also reach temperatures up to 4,000°C, hot enough to ignite clothing and cause additional flame burns.
- Radiation burns come from ultraviolet light (sunburn), radiation therapy, or nuclear exposure. Around 85% of patients undergoing radiation therapy develop a moderate to severe skin reaction that can include blistering and ulceration.
Burn Depth: First Through Fourth Degree
Burns are classified by how deep the damage extends into your skin.
First-degree burns affect only the epidermis. A typical sunburn is a first-degree burn. The skin turns red and hurts but doesn’t blister. These heal within a week without scarring.
Second-degree burns reach into the dermis. Because this layer contains nerve endings, these burns are intensely painful. Blisters form as fluid collects between the damaged layers. Superficial second-degree burns (affecting just the upper dermis) usually heal in two to three weeks. Deeper ones that damage more of the dermis take longer and carry a higher risk of scarring.
Third-degree burns destroy the full thickness of skin, extending into the subcutaneous fat. The burned area may look white, brown, or charred. Paradoxically, these burns may not hurt much at first because the nerve endings in the dermis have been destroyed. Third-degree burns cannot heal on their own and typically require skin grafting.
Fourth-degree burns extend past the skin entirely, damaging muscle, tendon, or bone. These are the most severe and life-threatening category.
Measuring How Much of the Body Is Burned
Doctors estimate the severity of a burn partly by calculating what percentage of the body’s surface area is affected, known as Total Body Surface Area (TBSA). The standard method divides the adult body into sections, each assigned a value of roughly 9%: the entire head is 9%, each arm is 9%, the chest is 9%, the abdomen is 9%, the upper back is 9%, the lower back is 9%, each thigh is 9%, each lower leg is 9%, and the groin is 1%. These percentages add up to 100%.
A quick rule of thumb for smaller burns: the palm of your hand (including fingers) represents about 1% of your body surface area. This can help you roughly gauge a burn’s size before getting medical attention.
What Makes a Burn Dangerous
Minor burns are painful but heal without lasting consequences. Larger or deeper burns trigger systemic problems that go far beyond the skin. When a large area of skin is destroyed, the body rapidly loses fluid through the open wound, which can lead to dangerously low blood volume and shock. At the same time, the massive inflammatory response can suppress the immune system, leaving the body vulnerable to infection.
Infection is the single most dangerous complication of a severe burn. Skin is the body’s primary barrier against bacteria, and losing a large area of it exposes underlying tissue to microbial invasion. Burn wound infections can progress to sepsis, a condition where the body’s response to infection spirals out of control and begins damaging its own organs. Sepsis and the resulting organ failure are the leading causes of death in severe burn patients.
Even when a burn isn’t immediately life-threatening, the body’s metabolic rate can surge dramatically as it tries to repair the damage. This hypermetabolic state increases calorie and protein needs, can break down muscle mass, and may persist for months after the initial injury.
Scarring After a Burn
Any burn that extends into the dermis can produce a scar. Most burn scars are flat and fade over time, but some develop into raised, thickened tissue. There are two types of abnormal scarring to be aware of.
Hypertrophic scars stay within the boundaries of the original wound. They’re raised and firm because the body produces about three times the normal amount of collagen during healing. Hypertrophic scars often improve on their own over months or years. Keloid scars, by contrast, grow beyond the edges of the original injury and do not regress. Keloids produce roughly 20 times the normal amount of collagen, arranged in a disorganized pattern rather than the orderly parallel fibers seen in normal healing. People with darker skin tones are at higher risk for keloids.
First Aid for a Burn
For a thermal burn, the most effective immediate step is cooling the wound under running cool water (around 15°C, or about 59°F) for at least 20 minutes. This should be done within the first three hours after injury. Cool water stops the burning process from continuing deeper into the tissue and reduces swelling. Avoid ice or ice water, which can cause frostbite on the already damaged skin.
Do not apply butter, toothpaste, or other home remedies. Cover the burn loosely with a clean, non-stick bandage. For chemical burns, remove contaminated clothing and rinse the area with large amounts of water, being careful not to spread the chemical to unaffected skin.
Burns That Need Specialized Care
Not every burn can be managed at home or even at a regular emergency room. The American Burn Association recommends referral to a specialized burn center for any of the following:
- Full-thickness (third-degree) burns of any size
- Partial-thickness (second-degree) burns covering 10% or more of the body
- Burns on the face, hands, feet, genitals, or over joints, because of the risk of functional impairment and scarring
- All chemical burns
- All high-voltage electrical injuries (1,000 volts or higher), plus lightning strikes
- Suspected inhalation injury, indicated by facial burns, singed nasal hair, or smoke exposure in an enclosed space
- All pediatric burns in children 14 and under, due to the complexity of pain management, wound care, and the need to screen for non-accidental trauma
Even low-voltage electrical burns that look minor on the surface warrant follow-up at a burn center, because internal damage can develop days later, and electrical injuries sometimes cause delayed vision problems.