Inorganic sun filters including zinc oxide and titanium dioxide are mineral active ingredients which are a key component of inorganic sunscreens since the 1980s.⁴ The size of these minerals can be in the range of non-nano or nanoparticles. Nanoparticles of zinc oxide are in the range of 200-400 nm and 150-300 nm for titanium dioxide.⁴ These particles provide sun protection due to their ability to absorb UV radiation with a small degree of scattering of light from reflection.⁴ Non-nano particles of zinc oxide are typically used in the formulation of homemade sunscreen. This leads to a higher SPF value, but decreases the amount of transparency of the sunscreen, leaving a white (from zinc oxide) or blue/white (if titanium dioxide) appearance.⁴ The FDA has approved up to 25% zinc oxide as the active ingredient in sunscreens.⁵

Internet users have several formulas they use in order to estimate the percentage of zinc oxide correlating to a value of SPF; however, no studies have been published to back up these values. In addition, the zinc oxide purchased by internet users is not specially coated, which causes the zinc oxide particles to clump together and does not provide evenly distributed protection when applied on the skin. These coated particles used in commercial sunscreens are advantageous in the formulation because they are non-greasy, inexpensive, and can provide an even distribution on the skin that does not degrade with exposure to UV radiation.⁴

In addition, inorganic UV filters including zinc oxide and titanium dioxide have few to no side effects in humans.⁴ There have been in vitro and in vivo experiments conducted with titanium dioxide resulting in increased mitochondrial dysfunction, oxidative stress, and hippocampal cell apoptosis if the inorganic filters are able to penetrate the stratum corneum to enter the dermis and eventually the blood supply.⁴ However, these inorganic filters do not typically penetrate through the skin to any significant degree.⁴

According to many homemade sunscreen forums, the use of beeswax is important in sunscreen to give the formulation a solid texture when mixed with various oils as well as giving the sunscreen water resistance through its occlusive properties.^6,7 Composed of hydrophobic substances including hydrocarbons, fatty acids, and esters, beeswax acts as an effective occlusive agent by forming a film on the skin’s surface and protecting against external irritants while buffering excess transepidermal water loss on the skin.^6,8 There are two types of beeswax usually used in cosmetic products, including yellow (Cera flava) and white (Cera alba).^6,8 In terms of safety, beeswax is generally thought to be nonirritating and has low comedogenic potential with some previously noted antimicrobial, anti-inflammatory, and antioxidant properties.⁶

Oils are used as the base of many homemade sunscreen recipes on the internet as they are easily absorbed by the skin and make lotions and creams very spreadable.⁹ The most commonly used oils in homemade sunscreen include olive oil, coconut oil, and almond oil. Previous research has found photoprotective properties in certain oils due to functional groups they possess that can absorb UV radiation.^10,11 A study on the SPF values of olive oil, coconut oil, and almond oil in vitro were 8, 7, and 5, respectively.¹² Other oils believed to confer higher SPF include carrot seed, coconut, raspberry seed, rosehip seed, and wheat germ oil. However, recent studies revealed that these same oils, including many vegetable oils, are not able to adequately absorb UVB light and lack photoprotective properties.^11,13,14 Though the utility of oils in sunscreen to provide SPF is low, their properties as emollients still make it a useful ingredient for homemade sunscreens.

Essential oils are added to homemade sunscreen for fragrance. However, certain essential oils contain a photoactive component known as furocoumarins, which can produce a phototoxic reaction when exposed to the sun.¹⁵ The most potent and well-known of these phototoxic substances is bergapten and its derivatives, including bergamottin, citropten, herniarin, and oxypeucedanin, which are found in oils derived from the herb species Seseli libanotis.^15,16 Furocoumarins are found in large quantities of various oils including lime oils, lemon oils, grapefruit oils, bergamot oils, and bitter orange oils, while other oils, such as angelica root, cumin, rue, Virginian cedarwood, and lemon verbena contain smaller quantities of these photoactive components.^16–20 Furocoumarins’ properties are responsible for the potential risk of a photosensitization reaction that may result after exposure to ultraviolet light.²¹ Though essential oils may be a component in some recipes of homemade sunscreens, a variation of ingredients may be used, and other formulations may be prepared with ingredients other than those mentioned throughout this text.

Sunscreens or lotions used to make homemade sunscreen should not contain vitamin A, as vitamin A increases the skin’s sensitivity to the sun.²² According to the American Academy of Dermatology, there is also a list of ingredients that still require more research before they are generally regarded as safe and effective (GRASE). Of these, ensulizole, octisalate, homosalate, octocrylene, octinoxate, oxybenzone, and avobenzone are commonly used in the U.S. while the ingredients cinoxate, dioxybenzone, meradimate, padimate O, and sulisobenzone are not commonly used in the U.S.²³

As presented on many of these internet blogs, some individuals who make sunscreen at home share different amounts of powder zinc oxide equating to specific SPF values that have not been reported through any formal testing or research. A blog by the name of Modern Hippie Inc. claims that about 0.27 ounces of zinc oxide equates to an SPF of 2-5 and 0.68 ounces to an SPF of 6-11, while another recipe by Don’t Waste the Crumbs reports a conversion of one ounce of zinc oxide to an SPF of 20. Despite an effort to provide readers with a reliable conversion tool, the lack of scientific support or testing results in misleading information that is neither accurate nor reliable when determining the efficacy and safety of a homemade product.

A review of homemade sunscreen ingredients from the top 50 Google search results, which included a combination of blog posts and social media videos, highlights distinct patterns in ingredient selection (Table 2). Out of 50 homemade sunscreen recipes, coconut oil (98%), shea/cocoa butter (92%), and beeswax (74%) were the most common included ingredients, likely serving as the primary base components in homemade sunscreen formulations. Despite limited scientific validation, certain oils were specifically included for their perceived SPF benefits. Carrot seed oil (50%) and red raspberry seed oil (28%) were among the most frequently recommended for their high SPF claims, with reported mean SPF values reaching 37.4 and 39.9, respectively. Non-nano zinc oxide powder (100%) was included in all homemade sunscreen recipes for its sun-protective properties with varying concentrations across recipes. The mean SPF claim was 18.3 with a range of 2-50 SPF, depending on the amount of zinc oxide powder used. Non-nano titanium dioxide (12%) was mentioned less often, but 6 homemade recipes included titanium dioxide with zinc oxide powder. Essential oils (46%) were included in many recipes as fragrance and cocoa powder (4%) was recommended to be added for darker skin tones.

274829 Table 1.

274830 Table 2.

SPF, UVA/UVB, FDA

None

Not applicable

Not required