Sunburn

Sunburn is a form of radiation burn that affects living tissue, such as skin, resulting from an overexposure to ultraviolet (UV) radiation, usually from the Sun. It is an inflammatory response in the tissue triggered by direct DNA damage by UV radiation. When the cells' DNA is overly damaged by UV radiation, type I cell-death is triggered, and the tissue is replaced. Sunburn increases the risk of various skin cancers, including melanoma, basal-cell carcinoma, and squamous-cell carcinoma.

A sunburnt neck

Signs and Symptoms

Blisters on a sunburned shoulder

Initial symptoms of sunburn include redness and varying degrees of pain, correlating with the duration and intensity of sun exposure. Other symptoms can include blistering, swelling, itching, peeling skin, rash, nausea, fever, chills, and fainting. Heat is produced from capillaries close to the skin surface, making the affected area warm to the touch. Blistering indicates a second-degree sunburn.

Minor sunburns cause slight redness and tenderness, whereas more severe cases can cause painful blistering, potentially requiring hospital care. Sunburn can develop in less than 15 minutes of sun exposure, with pain peaking 6 to 48 hours after exposure. The burn evolves over 1 to 3 days, sometimes followed by peeling skin after 3 to 8 days.

Causes

The cause of sunburn is the direct damage that a UVB photon can induce in DNA (left). One of the possible reactions from the excited state is the formation of a thymine-thymine cyclobutane dimer (right).

Sunburn is caused by UV radiation from the Sun and artificial sources like tanning lamps and welding arcs. The damage is mainly the formation of a thymine dimer in DNA. The body responds to this damage by triggering several defence mechanisms, including DNA repair, apoptosis, and increased melanin production.

Skin type, age, and certain genetic conditions affect susceptibility to sunburn. Fitzpatrick's skin phototypes classification describes the normal variations of skin responses to UV radiation. People with lighter skin tones and limited tanning capacity have a greater risk of sunburn.

Diagnosis

A sunburned leg below the shorts line

Sunburn diagnosis includes considering the duration and intensity of UV exposure, medication use, history of dermatologic disease, and nutritional status. Differential diagnoses include photoallergic and phototoxic reactions, phytophotodermatitis, polymorphic light eruption, solar urticaria, and skin diseases exacerbated by sunlight.

Prevention

Sunburn effect (as measured by the UV Index) is the product of the sunlight spectrum at the Earth's surface (radiation intensity) and the erythemal action spectrum (skin sensitivity). Long-wavelength UV is more prevalent, but each milliwatt at 295 nm produces almost 100 times more sunburn than at 315 nm.

Skin peeling on the upper arm as a result of sunburn – the destruction of lower layers of the epidermis causes rapid loss of the top layers.

The most effective way to prevent sunburn is to reduce UV radiation exposure. Recommendations include limiting sun exposure between 10 am and 4 pm, seeking shade, wearing sun-protective clothing, using sunscreen, and avoiding tanning beds. The UV Index can help gauge the strength of sunlight and the potential risk of sunburn.

Sunscreens are rated by their sun protection factor (SPF), with higher ratings indicating better protection. Broad-spectrum sunscreens protect against both UVA and UVB rays. Effective sunscreen use includes application 15 to 30 minutes before exposure, reapplication after swimming or sweating, and choosing products with SPF 30 or higher.

Treatment

Tanning of the forearm (visible darkening of the skin) after extended sun exposure.

The primary treatment for sunburn is avoiding further sun exposure. Time is the best healer, with most sunburns resolving in a few weeks. Recommended treatments include cool baths or showers, soothing moisturisers with aloe vera or soy, anti-inflammatory medications like ibuprofen or aspirin, and staying hydrated. Blisters should not be popped to allow natural healing. Protective clothing should be worn to prevent further damage.

NSAIDs and aspirin can decrease pain and redness, while local anaesthetics like benzocaine are contraindicated. Topical steroids may provide relief for sore areas, though their efficacy is debated. Applying cool, wet cloths and moisturisers containing aloe vera or soy can help alleviate discomfort.

Self-assessment MCQs (single best answer)

What is sunburn primarily caused by?

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Which type of skin cancer is NOT commonly associated with sunburn?

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Which symptom indicates a second-degree sunburn?

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How long can it take for sunburn pain to peak after exposure?

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Which of the following is NOT a recommended method to prevent sunburn?

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What does the "SPF" in sunscreens stand for?

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Which of the following is NOT a primary treatment for sunburn?

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Which reaction from UV radiation can damage DNA and cause sunburn?

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What is the Fitzpatrick skin phototypes classification used for?

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When should sunscreen be applied to be most effective?

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