Step by Step
1st
First-degree burns — superficial
First-degree (superficial) burns damage only the epidermis. They appear red and dry, and are painful — sunburn is the classic example. They heal in 3-5 days with no scarring.
2nd
Second-degree burns — partial thickness
Second-degree (partial thickness) burns damage the epidermis plus part of the dermis. They produce blisters and are very painful, since nerve endings remain intact and exposed. Healing takes 2-3 weeks and may result in scarring.
3rd
Third-degree burns — full thickness, and no pain
Third-degree (full thickness) burns destroy the epidermis, dermis, and possibly the hypodermis. The skin appears leathery, waxy, or charred, and — critically — these burns are not painful, since the nerve endings themselves have been destroyed. Third-degree burns require skin grafting.
Rule
The Rule of Nines — estimating burn surface area
The Rule of Nines is used to estimate the percentage of body surface area affected by a burn: the head is 9%, each arm is 9%, each leg is 18%, the anterior trunk is 18%, the posterior trunk is 18%, and the perineum is 1%. A critical burn is defined as greater than 25% body surface area with second-degree burns, or any third-degree burn at all. The major risks associated with severe burns are infection and fluid loss.
A patient with a third-degree burn covering their entire hand and forearm reports no pain at all in the burned area — this absence of pain is actually a concerning clinical sign, since it indicates the nerve endings themselves have been destroyed, marking full-thickness tissue damage rather than a more superficial injury.
Applied Walkthrough
1
A patient arrives at the emergency room with a burn injury, and the triage nurse notes the patient reports the burned area doesn't hurt at all, despite the skin appearing charred and leathery.
2
Ask: is the absence of pain actually a reassuring sign here? No — counterintuitively, the lack of pain is a serious warning sign rather than a reassuring one. It indicates a third-degree (full-thickness) burn, where the nerve endings themselves have been destroyed, unlike a first- or second-degree burn, where intact nerve endings would produce significant pain.
3
This is exactly why burn severity assessment can't rely on pain level alone — a patient in severe pain might actually have a less severe (though still significant) second-degree burn, while a patient reporting no pain at all in a charred area may have the most severe, full-thickness third-degree damage.
4
Understanding this counterintuitive relationship between burn depth and pain level is critical for correctly triaging burn severity, rather than assuming that more reported pain always corresponds to worse tissue damage.
Exam Application
Exams test the depth and features of each burn degree (first: epidermis only, red/painful, no scarring; second: epidermis + part of dermis, blisters/very painful, may scar; third: full thickness, leathery/no pain, requires grafting), the Rule of Nines percentages for estimating burn surface area, and the counterintuitive relationship between burn severity and pain level.
⚠ Common Trap
The most common trap is assuming a burn that doesn't hurt must be less severe than one that does. Third-degree burns are actually the most severe of the three types, and specifically don't hurt because the nerve endings have been destroyed — the absence of pain reflects greater tissue damage, not less.
✓ Quick Self-Check
1. What layer(s) does a first-degree burn damage, and what are its clinical features?
Only the epidermis; it appears red and dry, and is painful, healing in 3-5 days with no scarring.
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2. What layer(s) does a second-degree burn damage, and what are its clinical features?
The epidermis plus part of the dermis; it produces blisters and is very painful, healing in 2-3 weeks with possible scarring.
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3. What layer(s) does a third-degree burn damage, and why is it not painful?
The epidermis, dermis, and possibly the hypodermis; it's not painful because the nerve endings have been destroyed.
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4. According to the Rule of Nines, what percentage of body surface area does each leg represent?
18%.
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5. What defines a 'critical' burn?
Greater than 25% body surface area with second-degree burns, or any third-degree burn at all.
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