Sunscreens prevent skin damage by reflecting, absorbing or scattering ultraviolet radiation.

Sun protection factor (SPF)-number equal to the ratio of doses of UV (mostly UVB radiation) that results in erythema with protection to the doses that cause erythema without protection.

Sunscreen is regulated as an over-the-counter medication by the FDA.

Sunscreens are indicated for the prevention of sunburn and skin cancer.

Sun protection factor (SPF)-SP 2 equals a 50% blockage, 15 equates to a 93% block and SPF 45 equals a 98% block.

Sun protection factor (SPF)-15 is minimal recommendation for protection.

American Academy of dermatology recommends applying water-resistant sunscreen SPF 30 or higher with both ultraviolet A (320-400 nm) and ultraviolet B 290-320 nm) protection.

Sun protection factor (SPF)-most people apply inadequate amounts and less often than recommended.

Sun protection factor (SPF)-daily application and reapplication after swimming and sweating is recommended.

No available products adequately shield skin from UV-A rays which constitute about 95% of the ultraviolet light that reaches the skin.

The higher the SPF rating, the lower the amount of direct DNA damage. 

The sun protectant factor (SPF) is correct only if 2 mg of sunscreen is applied per square cm of exposed skin. 

This translates into about 28 mL (1 oz) to cover the whole body of an adult male, which is much more than many people use in practice.

Regular sunscreen use prevents cutaneous squamous cell carcinoma and melanoma (Robinson JK et al).

It has been estimated that over 1/3 of melanomas in the United States and Australia could be prevented with regular sunscreen use.

The clinical relevance of systemic exposure is not known.

Sunscreen ingredients fall into two categories: mineral or chemical.

Sunscreens function as chemicals such as oxybenzone and dioxybenzone (organic sunscreens) or opaque materials such as zinc oxide or titanium oxide (inorganic sunscreens) that both mainly absorb UV radiation. 

Mineral sunscreens contained physical UV filters, such as zinc oxide and titanium dioxide, offers broad-spectrum coverage by reflecting or refracting UV radiation from the skin.

Chemical sunscreens contain UV filters that absorbUV radiation and, when used in combination provides equal if not superior broad-spectrum UV filtration compared with mineral sunscreens.

Chemical and mineral sunscreens vary in the wavelengths of UV radiation blocked. 

Broad-spectrum sunscreens contain filters that protect against UVA radiation as well as UVB. 

Although UVA radiation does not primarily cause sunburn, it does contribute to skin aging and an increased risk of skin cancer.

Mineral sunscreen are more likely to leave chalky white residue on the skin.

Chemical sunscreens are found in the majority of sunscreen formulations.

Sunscreen formulations are a $1.95 billion industry in the US.

In a clinical study it was demonstrated systemic exposure of the four commonly used sunscreen ingredients, indicating their plasma concentration exceeded 0.5 ng per mL.

Presently, absorption of sunscreens raises concerns about their safety and their effects.

In a randomized clinical trial of 48 healthy participants, it was found that sunscreen active ingredients are systemically absorbed following a single application of these products on day one and multiple applications through the IV (Matta MK).

Under maximal use conditions 4 chemical UV filters-avobenzone, oxybemzone, octocrylene and ecamsule we are absorbed through the skin and achieve systemic levels exceeding FDA threshold for safety testing.
In another study 6 sunscreen filters achieved plasma concentrations significantly above FDA  threshold after a single application.
Concentrations of sunscreen filters increased after each day of application, suggesting accumulation within the blood.
The half-life of these filters if the maximal use range between 27 hours and 157 hours depending on the spray type.
Studies of sunscreen absorption do not provide any evidence that chemical sunscreens cause harm.
Sunscreens with SPF 50+ decreases cutaneous production of vitamin D 25 (OH) D3 and likely decreases serum levels.
Regularly applied sunscreens for a five year period has been associated with a lower incidence of primary melanomas up to 10 years following the conclusion of a trial.

Sunscreen used in adults 18-40 years old regularly used in childhood reduced the risk of developing melanoma  by 40% compared to those who rarely used sunscreen.

There is little evidence that it is effective in preventing basal cell carcinoma.

Typical use of sunscreen does not usually result in vitamin D deficiency, but extensive usage may.

Leave a Reply

Your email address will not be published. Required fields are marked *