By Hanna Jang, PA-S
The American Academy of Dermatology recommends the choice of sunscreen products that have sun protection factor (SPF) of 30 or higher, broad-spectrum coverage, and water or sweat resistance. In addition to SPF and performance characteristics, the cosmetic appeal of sunscreen products appears to be an important selection criterion used by consumers.
SPF — The SPF value primarily measures the level of protection against ultraviolet B (UVB) and ultraviolet A2 (UVA2) and is based on the ratio of the minimal erythema dose on sunscreen-protected skin compared with unprotected skin. The relationship between SPF and absorption of UVB radiation is not linear. In fact, when applied in sufficient amount, the amount of UVB radiation absorbed by SPF 15, 30, and 50 sunscreen products is 93, 97, and 98 percent, respectively. However, since the amount of UVB delivered to the skin through a sunscreen is reduced in a nearly linear way with increasing SPF, a sunscreen with SPF of 30 is twice as protective as one of 15 in preventing erythema. Products with SPF >50 provide only a negligible increase in the protection from UV radiation.
Water resistance — Water (and sweat) resistance is a key feature to consider when selecting a sunscreen product to use while working or practicing sports or recreational activities outdoors . The terms "water-resistant" and "very water-resistant" mean that the SPF is maintained after 40 or 80 minutes of activity in water or sweating, respectively.
For infants and young children — The American Academy of Pediatrics recommends avoiding the use of sunscreen products in infants younger than six months. However, when adequate clothing and shade are not available, a minimal amount of sunscreen with at least 15 SPF can be applied to small areas, such as the infant's face and the back of the hands.
Since infants have an immature skin barrier, sunscreen products should be non irritating to the skin and eyes and have a low sensitization potential.
Oil-based emulsions of inorganic filters (ie, titanium dioxide, zinc oxide) are preferred to organic filters for infants and children because they offer broad-spectrum protection and have minimal irritation, sensitization, and skin penetration potential.
PROPER USE OF SUNSCREENS — Sunscreens must be applied liberally, repeatedly, and to all sun-exposed parts of the skin to provide effective protection. To achieve the full sun protection factor (SPF) value on the product label, the amount (2 mg/cm2) of sunscreen necessary to cover sun-exposed skin of an average-sized adult when on a beach vacation is approximately equivalent to the amount required to fill a 1-ounce (30 mL) shot glass or to 6 teaspoons. However, larger amounts, up to 45 mL or 9 teaspoons, may be needed for optimal coverage.
The "teaspoon rule" — It involves the application of 1 teaspoon (visually measured) of sunscreen to the face and neck area, a total of 2 teaspoons to the front and back torso, 1 teaspoon to each upper extremity, and 2 teaspoons to each lower extremity.
Timing — Timing of application is important. Sunscreens should be applied 15 to 30 minutes before sun exposure to allow the formation of a protective film on the skin. It is recommended to wait for at least a few minutes (ideally, 10 to 20) following sunscreen application before dressing .Reapplication at least every two hours is necessary.
BENEFITS OF SUNSCREENS :
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