Sunscreens are topical agents designed to protect the skin from ultraviolet (UV) radiation. Exposure to UV radiation (UVR) is a significant contributor to skin aging and the primary cause of skin cancers, such as basal cell carcinoma, squamous cell carcinoma, and melanoma. Effective sun protection, including the use of sunscreen and sun-protective clothing, is crucial in mitigating these harmful effects. While the term “sunblock” was once used interchangeably with sunscreen, it is now considered misleading, as no sunscreen can block 100% of UVR.
UV radiation is categorized into three types: ultraviolet A (UVA), ultraviolet B (UVB), and ultraviolet C (UVC). UVC is absorbed by the Earth’s atmosphere, leaving UVA and UVB as the primary concerns for skin protection. Sunscreens are formulated to shield the skin from the damaging effects of both UVA and UVB radiation. It is advisable to apply sunscreen daily when the UV index is forecasted to reach 3 or higher.
Chemical sunscreens function by absorbing UVR, while physical sunscreens (also known as inorganic filters, blockers, or mineral-based sunscreens) were traditionally thought to reflect or scatter UVR. However, studies have shown that physical sunscreens primarily protect by absorbing UVR, similar to chemical sunscreens.
Chemical sunscreens, also known as organic filters or absorbers, typically contain a blend of ingredients to provide broad-spectrum protection. Common agents include:
– Aminobenzoic acid derivatives (e.g., Padimate O)
– Benzophenones (e.g., oxybenzone)
– Cinnamates (e.g., octocrylene)
– Salicylates (e.g., homosalate)
Photostable agents like octocrylene, bemotrizinol, and bisoctrizole are often added to enhance the stability of these sunscreens.
Physical sunscreens usually contain inorganic metal oxides such as titanium dioxide and zinc oxide. These ingredients:
– Reflect photons in the visible light range and absorb UV radiation
– Provide broad-spectrum UVA and UVB coverage
– Are chemically inert, safe, and photostable
Microsized or ultrafine grades (nanoparticles) of titanium dioxide and zinc oxide improve application ease and reduce visible residue on the skin. Although there are concerns about the potential toxic or carcinogenic effects of nanoparticles, no adverse effects have been demonstrated, and the benefits of sun protection outweigh these theoretical risks.
Sunscreens can be classified as primary or secondary. Primary sunscreens are designed mainly for sun protection, whereas secondary sunscreens, such as those in makeup, offer sun protection as a secondary benefit.
Recent FDA regulations have proposed that titanium dioxide and zinc oxide are safe and effective, whereas PABA and trolamine salicylate are not. More data is needed to determine the safety of other ingredients like padimate O, oxybenzone, and avobenzone.
Some chemical sunscreen ingredients, including oxybenzone, octocrylene, octinoxate, and avobenzone, have been banned in certain locations due to their negative impact on coral reefs. In these areas, mineral sunscreens containing zinc oxide and titanium dioxide are preferred. It is important to check local regulations for specific details.
Sunscreen labels provide information about UVA and UVB protection. The Sun Protection Factor (SPF) rating pertains primarily to UVB protection, which is the main cause of sunburn. The higher the SPF number, the greater the expected protection:
– SPF 15 provides about 94% UVB protection
– SPF 30 offers 97% UVB protection
– SPF 50+ offers 98% UVB protection
UVA protection is often indicated by terms such as “broad spectrum” and measured using methods like the UVA Protection Factor (UVA-PF) and critical wavelength (CW).
Accurate labelling helps consumers choose products that offer the best protection. Terms like “sunblock,” “waterproof,” or “sweatproof” are considered misleading and are no longer permitted. Effective sunscreen use involves applying the product in adequate quantities and reapplying it regularly, especially after swimming or sweating.
Sunscreens offer significant benefits, including reducing the risk of sunburn, skin cancer, hyperpigmentation, and photoaging. However, it is crucial to apply them correctly and use other sun protection measures such as wearing protective clothing and seeking shade.
Concerns about systemic absorption and potential endocrine effects of certain chemical sunscreens are still being researched. Despite these concerns, the established benefits of sun protection with sunscreens are considered to outweigh potential risks.
Sunscreens are an essential component of a comprehensive sun protection strategy. By understanding the types, benefits, and proper application of sunscreens, individuals can effectively protect their skin from harmful UV radiation and maintain overall skin health.
