Sunburn is an acute skin inflammation following overexposure to UV radiation. Redness (erythema), warmth, oedema (accumulation of fluid), and tenderness to the touch are characteristic of sunburn, with pain and blistering characteristic of severe sunburn. Whole of body sunburn may result in systemic symptoms such as headaches and nausea.
Sunburn is influenced by a variety of factors, including skin type, skin hydration, age and anatomical site (skin thickness and previous UV exposure). Environmental factors include UV wavelength and dose, geographical factors (altitude, latitude, time of day), presence of UV reflective surfaces (e.g. snow, water) and climatic factors (wind, temperature, humidity).
UV radiation: wavelength and dose
Sunburn is a product of total UV radiation dose and is equally likely to result from both a high UV dose and from exposure to lower levels of UV radiation over an extended period of time. The smallest dose, causing a perceptible erythema (reddening of the skin) 24 hours after exposure, is referred to as the minimal erythema dose (MED). The standardised measurement of an erythemogenic dose of UV radiation is the standard erythema dose (SED). One SED is equivalent to an exposure of 100J/m2 and is independent of skin type. Therefore the same exposure dose in SED that causes erythema in fair skin may have no effect on darker skin. Although UVB is a thousandfold more effective in producing sunburn than UVA, because solar energy reaching the earth is primarily UVA (315 – 400nm), it also has an important contribution to sunburn and other harmful effects of UV radiation. Shorter wavelengths of UVA (315-340nm) are more erythemogenic than the remainder of the UVA waveband.
Although sunburn can occur in both fairly and darkly pigmented individuals, skin type determines how susceptible an individual is to sunburn. Moderately pigmented skin requires 3-5 times the exposure, and darkly pigmented skin up to 30 times the exposure, compared with the amount of time required to induce sunburn in those with fair pigmentation. As defined by the Fitzpatrick skin phototype classification (see Table 1), skin types IV-VI are unlikely to experience sunburn following excess UV radiation exposure.
Table 1: Fitzpatrick skin phototypes I-VI  (as adapted by ARPANSA)
|I||Always burns, never tans (pale white skin)|
|II||Always burns easily, tans minimally(white skin)|
|III||Sometimes mild burn, tans about average (light brown skin)|
|IV||Rarely burns, tans more than average (with ease) (moderate brown skin)|
|V||Rarely burns, tan more than average (with ease) (dark brown skin)|
|VI||Never burns (deeply pigmented dark brown or black skin)|
Sunburn duration is also a function of skin type. Immediate UVB-induced sunburn can occur in individuals with skin types I and II, but usually the sunburn response is delayed until six to 24 hours after exposure. Therefore, it is at this 24-hour endpoint that sunburn is clinically defined. UVB-induced sunburn may last for one to two weeks for fair skin types I and II, while for skin type V individuals it may disappear as soon as three days after exposure. UVA sunburn shows immediately, fading then reappearing after six hours and peaking at 24 hours, or even longer.
Sunburn may be followed by desquamation (skin peeling) and, depending on skin type, tanning. Certain medications - including some antibiotics, antihistamines, cardiovascular drugs, diuretics, antidiabetic drugs, and antidepressants - can increase photosensitivity, which makes people more susceptible to sunburn.
Sunburn in Australia
Sunburn can occur in as little as 15 minutes on a fine January day in Australia. Since UVR passes easily through water, swimming in either the sea or open-air pools offers little protection against sunburn.
The latest national data for adolescents and adults show that approximately one in five adolescents and one in eight adults were sunburnt on a summer weekend when they were outdoors. Weekend sunburn during peak UV radiation times significantly decreased among adolescents and adults relative to surveys conducted in 2003-04 and 2006-07, after adjusting by temperature and cloud, and UV Index levels. Both adolescents and adults had a similar likelihood of being sunburnt whether outdoors at the beach or a sporting ground.
- Armstrong BK. How sun exposure causes skin cancer: An epidemiological perspective In: Hill D, Elwood JM, English D. Prevention of Skin Cancer. Dordrecht, The Netherlands: Kluwer Academic Publishers; 2004. p. 89-116.
- Whiteman DC, Whiteman CA, Green AC. Childhood sun exposure as a risk factor for melanoma: a systematic review of epidemiologic studies. Cancer Causes Control 2001 Jan;12(1):69-82 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/11227927.
- Pfahlberg A, Kölmel KF, Gefeller O, Febim Study Group. Timing of excessive ultraviolet radiation and melanoma: epidemiology does not support the existence of a critical period of high susceptibility to solar ultraviolet radiation- induced melanoma. Br J Dermatol 2001 Mar;144(3):471-5 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/11260001.
- Veierød MB, Adami HO, Lund E, Armstrong BK, Weiderpass E. Sun and solarium exposure and melanoma risk: effects of age, pigmentary characteristics, and nevi. Cancer Epidemiol Biomarkers Prev 2010 Jan;19(1):111-20 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/20056629.
- Cust AE, Jenkins MA, Goumas C, Armstrong BK, Schmid H, Aitken JF, et al. Early-life sun exposure and risk of melanoma before age 40 years. Cancer Causes Control 2011 Jun;22(6):885-97 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/21472378.
- Kennedy C, Bajdik CD, Willemze R, De Gruijl FR, Bouwes Bavinck JN, Leiden Skin Cancer Study. The influence of painful sunburns and lifetime sun exposure on the risk of actinic keratoses, seborrheic warts, melanocytic nevi, atypical nevi, and skin cancer. J Invest Dermatol 2003 Jun;120(6):1087-93 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/12787139.
- Hönigsmann H. Erythema and pigmentation. Photodermatol Photoimmunol Photomed 2002 Apr;18(2):75-81 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/12147040.
- International Agency for Research on Cancer. Solar and ultraviolet radiation. Vol. 100D. Lyon, France: International Agency for Research on Cancer; 2012.
- Fitzpatrick TB. The validity and practicality of sun-reactive skin types I through VI. Arch Dermatol 1988 Jun;124(6):869-71 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/3377516.
- Dubakiene R, Kupriene M. Scientific problems of photosensitivity. Medicina (Kaunas) 2006;42(8):619-24 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/16963827.
- Samanek AJ, Croager EJ, Gies P, Milne E, Prince R, McMichael AJ, et al. Estimates of beneficial and harmful sun exposure times during the year for major Australian population centres. Med J Aust 2006 Apr 3;184(7):338-41 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/16584368.
- Diffey BL. Human exposure to ultraviolet radiation In: Hawk JLM. Photodermatology. London: Oxford University Press; 1999.
- Volkov A, Dobbinson S, Wakefield M, Slevin T. Seven-year trends in sun protection and sunburn among Australian adolescents and adults. Aust N Z J Public Health 2013 Feb;37(1):63-9 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/23379808.
- Volkov A, Dobbinson SJ. 2010–11 National Sun Protection Survey Report 2. Australians’ sun protective behaviours and sunburn incidence on summer weekends, 2010–11 and comparison with 2003–04 and 2006-07. Melbourne, Australia: Centre for Behavioural Research in Cancer, Cancer Council Victoria; 2011 Oct.