[13] To effectively protect against all the potential damages of UV light, the use of broad-spectrum sunscreens (covering both UVA and UVB radiation) has been recommended.

[15] Among the nomadic sea-going Sama-Bajau people of the Philippines, Malaysia, and Indonesia, a common type of sun protection is a paste called borak or burak, which was made from water weeds, rice and spices.

In Madagascar, a ground wood paste called masonjoany has been worn for sun protection, as well as decoration and insect repellent, since the 18th century, and is ubiquitous in the Northwest coastal regions of the island to this day.

[37] A 2013 study concluded that the diligent, everyday application of sunscreen could slow or temporarily prevent the development of wrinkles and sagging skin.

[38] A study on 32 subjects showed that daily use of sunscreen (SPF 30) reversed photoaging of the skin within 12 weeks and the amelioration continued until the end of the investigation period of one year.

[39] Sunscreen is inherently anti-ageing as the sun is the number one cause of premature ageing; it therefore may slow or temporarily prevent the development of wrinkles, dark spots, and sagging skin.

[40] In February 2019, the US Food and Drug Administration (FDA) started classifying already approved UV filter molecules into three categories: those which are generally recognized as safe and effective (GRASE), those which are non-GRASE due to safety issues, and those requiring further evaluation.

The remaining FDA approved active ingredients were put in the third category as their manufacturers have yet to produce sufficient safety data — despite the fact that some of the chemicals have sold in sunscreen products for more than 40 years.

[24][46] Regulators, such as the TGA and the FDA, have also been concerned with recent reports of contamination in sunscreen products with known possible human carcinogens such as benzene and benzophenone.

[49] VOC's (Volatile Organic Compounds) such as benzene, are particularly harmful in sunscreen formulations as many active and inactive ingredients can increase permeation across the skin.

For example, "SPF 15" means that 1⁄15 of the burning radiation will reach the skin, assuming sunscreen is applied evenly at a thick dosage of 2 milligrams per square centimeter[65] (mg/cm2).

[86] As part of revised guidelines for sunscreens in the EU, there is a requirement to provide the consumer with a minimum level of UVA protection in relation to the SPF.

[3] In the UK and Ireland, the Boots star rating system is a proprietary in vitro method used to describe the ratio of UVA to UVB protection offered by sunscreen creams and sprays.

In August 2007, the FDA put out for consultation the proposal that a version of this protocol be used to inform users of American product of the protection that it gives against UVA;[76] but this was not adopted, for fear it would be too confusing.

Most organic compounds in sunscreens slowly degrade and become less effective over the course of several years even if stored properly, resulting in the expiration dates calculated for the product.

Furthermore, adding antioxidants to sunscreen can amplify its ability to reduce markers of extrinsic photoaging, grant better protection from UV induced pigment formation, mitigate skin lipid peroxidation, improve the photostability of the active ingredients, neutralize reactive oxygen species formed by irradiated photocatalysts (e.g., uncoated TiO₂) and aid in DNA repair post-UVB damage, thus enhancing the efficiency and safety of sunscreens.

[120][121][113] Similarly, film-forming polymers like polyester-8 and polycryleneS1 have the ability to protect the efficacy of older petrochemical UV filters by preventing them from destabilizing due to extended light exposure.

Further research has shown that sunscreens with added iron oxide pigments and/or pigmentary titanium dioxide can provide the wearer with a substantial amount of HEVL protection.

Mica was discovered to have significant synergistic effects with UVR filters when formulated in sunscreens, in that it can notably increase the formula's ability to protect the wearer from HEVL.

[128] There is a growing amount of research demonstrating that adding various vitamer antioxidants (eg; retinol, alpha tocopherol, gamma tocopherol, tocopheryl acetate, ascorbic acid, ascorbyl tetraisopalmitate, ascorbyl palmitate, sodium ascorbyl phosphate, ubiquinone) and/or a mixture of certain botanical antioxidants (eg; epigallocatechin-3-gallate, b-carotene, vitis vinifera, silymarin, spirulina extract, chamomile extract and possibly others) to sunscreens efficaciously aids in reducing damage from the free radicals produced by exposure to solar ultraviolet radiation, visible light, near infrared radiation and infrared-a radiation.

[85] A later study found a significant exponential relation between SPF and the amount of sunscreen applied, and the results are closer to linearity than expected by theory.

[141] On 1 January 2020, Palau banned the manufacturing and selling of sun cream products containing any of the following ingredients: benzophenone-3, octyl methoxycinnamate, octocrylene, 4-methyl-benzylidene camphor, triclosan, methylparaben, ethylparaben, butylparaben, benzyl paraben, and phenoxyethanol.

The animal studies evaluate the potential for inducing carcinogenesis, genetic or reproductive harm, and any toxic effects of the ingredient once absorbed and distributed in the body.

Two previously approved UV filters, para-aminobenzoic acid (PABA) and trolamine salicylate, were reclassified as not GRASE due to safety concerns and have consequently been removed from the market.

[153] Some sunscreen active ingredients have been shown to cause toxicity towards marine life and coral, resulting in bans in different states, countries and ecological areas.

Factors like temperature changes, invasive species, pollution, and detrimental fishing practices have previously been highlighted as threats to coral health.

[162] Echoing Hawaii's initiative, other regions including Key West, Florida,[163] the U.S. Virgin Islands,[164] Bonaire, and Palau[165] have also instituted bans on sunscreens containing oxybenzone and octinoxate.

In a 2015 study, titanium dioxide nanoparticles, when introduced to water and subjected to ultraviolet light, were shown to amplify the production of hydrogen peroxide, a compound known to damage phytoplankton.

[167] Further probing the matter, a 2008 investigation examining a variety of sunscreen brands, protective factors, and concentrations revealed unanimous bleaching effects on hard corals.

When assessing individual compounds prevalent in sunscreens, substances such as butylparaben, ethylhexylmethoxycinnamate, benzophenone-3, and 4-methylbenzylidene camphor induced complete coral bleaching at even minimal concentrations.