Sunscreen 101
The smell of sunscreen takes me back to childhood days, when we would slather it all over our skin before heading outside into the sun to play. In those times, we didn't care if it left a "white cast", was greasy, or had that familiar "sunscreen" smell - all it needed to do was protect our skin!
Sunscreen is one of the most important skincare products you can use - all the daily serums, lotions, and creams aimed at smoothing, rejuvenating and enhancing skin health cannot do what sunscreen does, which is help prevent skin aging and skin damage from those notorious UV rays. It's important to recognize too that using sunscreen is a luxury, as it can be expensive when using regularly. Keep on reading if you are curious how sunscreens work, the difference between physical and chemical sunscreen, general recommendations, ingredients, and what to look for when choosing a sunscreen for your skin.
General Recommendations
The goal of sunscreen is to reduce burning, skin tanning (which is still sun damage), photoaging, and actinic keratosis[1]. Also remember that sunscreen is an important ADDITION to other sun safety measures (wide brimmed hat, seeking shade, etc). The Canadian Dermatology Association recommends a sunscreen[1]:
Has an SPF of at least 30
Is broad-spectrum, for both UVA + UVB protection
Is non-comedogenic (won’t block pores), non-irritating, and hypoallergenic
Should have minimal or no fragrance
What is SPF?
SPF stands for Sun Protection Factor, which is the lowest amount of energy that causes skin redness (usually from UVB) WITH the sunscreen on the skin, divided by the lowest amount of energy that causes redness WITHOUT sunscreen[1]. The SPF of a product is a combination of its UV absorption range, maximum absorbance, concentration of active ingredients, molar absorptivity (amount of radiant energy sunscreen can absorb), pH, and the solvent used[2].
In Canada, if a product is broad spectrum and has an SPF 15+, it can claim to decrease the risk of skin cancer and early skin aging caused by the sun, if used as directed with other sun protection measures[1]. If the SPF is less than 15 or it isn’t broad spectrum, it can only claim to help prevent sunburn (not skin cancer). If water-resistant, it is either for 40 or 80 minutes[1]. Also be aware that extreme temperatures (eg very hot car) may separate/discolour the formulation and affect sunscreen efficacy[1].
There is limited data showing that very high SPF (eg. 50-100) may have some increased protection in controlled conditions; double the SPF does not mean double the protection, which has led to concerns regarding misinterpretation from consumers[1]. An SPF 30 sunscreen blocks about 97% of UVB rays. As SPF mostly relates to UVB (the cause of most sunburns), it’s important to realize that a high SPF may not be as protective overall as a sunscreen with a lower SPF and broad spectrum coverage[1]!
Types of Sunscreen
Physical (Inorganic) Sunscreen
Physical sunscreens contain either titanium dioxide or zinc oxide as the active ingredient[1]. They reflect and scatter both UV and visible light, and can help protect against light-induced photosensitivity[1]. Although both ingredients are broad spectrum (protect against UVA + UVB), microfine zinc oxide offers better UVA protection than titanium dioxide[3]. These physical sunscreens have less risk of sensitization than chemical sunscreens, but they may rub off easily or melt in heat[1]. Usually thicker and less cosmetically elegant, physical sunscreens may cause miliaria (a type of heat rash) or blocked follicles[1,3]. Recently, many physical sunscreens are being formulated to be more cosmetically appealing, containing micronized titanium dioxide and zinc oxide[1]. Tinted mineral sunscreens are also available, to help counteract any “white cast” of a mineral formulation.
Chemical (Organic) Sunscreen
This type of sunscreen absorbs UV light of various wavelengths, the range depending on the specific chemical used[1]. Often different active ingredients are combined to widen the UV spectrum that is covered and increase stability[1,3]. These sunscreens tend to be thinner and easier to apply than physical sunscreens, but are more likely to be irritating or sensitizing[1]. Common chemical sunscreen ingredients include benzophenones (eg oxybenzone), benzylidene camphor derivatives (eg Mexoryl SX), cinnamates (such as octinoxate, octocrylene), dibenzoylmethanes (eg avobenzone), and salicylates (such as homosalate, octisalate)[1].
Formulation
An oil-in-water or water-in-oil emulsion (eg a lotion or cream) are often greasy, while gels are less greasy but usually alcohol based and can be drying[1]. Sprays are usually applied incorrectly and should be rubbed in with hands (not sprayed and left to sit)[1]. Lip balms are also available with SPF for easy lip protection[1]. Solvents (what ingredients are dissolved in) in a sunscreen affect how stable it is and how well active ingredients bind to the skin; if you see alcohol as a solvent, it’s because it allows for the most rapid and deepest penetration through the epidermis[2].
Application
Sunscreen can be used for ages 6 months and up[1]. Under 6 months, avoid any direct sun exposure; use of sunscreen is not recommended unless directed by a clinician, as the skin of this age group may have different absorptive properties (immature metabolic and excretion pathways)[1,2].
Make sure to apply liberally 15-30 minutes before sun exposure (in order for active ingredients to bind to the skin) and include top of feet, ears, and lips[1,3]. Reapply after swimming/sweating[1]. Systemic absorption is small, especially with physical sunscreens, so both chemical and physical sunscreens are considered safe in pregnancy and breastfeeding[3].
In the real world, application usually ends up being 20-50% less than what is recommended, so an easy way to remember how much to use is the teaspoon (1 tsp = 5mL) rule[1]:
1 tsp for face, head and neck
1 tsp for 1 arm (shoulder to finger)
2 tsp for front and back of torso
2 tsp for leg front and back (hip to toes)
When applying other products, sunscreen should be applied FIRST. This includes insect repellent - if applied the same time as DEET, it may lower the SPF; whereas the efficacy of DEET is the same regardless of when it is applied[1].
Safety
The absorption of chemical sunscreens in humans is poorly documented, with inconclusive studies on the safety of ingredients and additives in sunscreen[1]. Current guidelines recommend continuing to use sunscreen given the extensive beneficial evidence. Regarding the environmental effect of sunscreens, about 25% of sunscreen is washed off in swimmers within 20 minutes of water exposure[1]. Further study is needed to determine any harmful effects on marine organisms.
A study in 2021 by Valisure, an analytical lab that performs chemical testing, detected levels of benzene (a known human carcinogen) in specific batches of sunscreen products[4]. Benzene is a volatile organic compound, and found all around us every day - for example, in gasoline and cigarette smoke. It’s a compound that used to be in paint as well - I studied it for my Master’s research! It is important to note that the presence of benzene in the tested batches was from contamination, and is not a regular component of sunscreens. Sometimes this happens with drug recalls as well, when quality control batch-testing of medication discovers an undesirable contaminant in the product. This normally leads to a recall of all medication within that lot. In summary, check the tables on the Valisure petition document for specific sunscreens and lot numbers, and if it’s not on the list, keep using your sunscreen!
What About Tanning?
"Sun bathing" or sun tanning is not recommended. Many people believe if you don't burn, the skin hasn't been damaged. Data indicates both carcinogenesis and photoaging can occur at doses of UV radiation below what is required to cause a sunburn (ie. doesn’t cause redness/appearance of a burn, but still damages the skin)[2]. Sun tanning and exposing unprotected skin repeatedly to the sun can increase the risk of skin aging, skin cancer, and other skin damage even if you don’t get a sunburn[2]. Opt for sunless tanning (“self-tanners”) instead if you are looking for a summer glow (post on these coming in the future), and check out The Deets on Sun Damage for more on why it’s important to protect the skin from the sun. Stay tuned for reviews of my favourite sunscreens!
References
Kleiman, N. Prevention and Treatment of Sun-Induced Skin Damage. Canadian Pharmacists Association. Revised April 12, 2021. Retrieved 25May2021 from eCPS.
Lexicomp. Sunscreens (Topical). AHFS Drug Information. Revised Feb 26, 2021. Retrieved 25May2021 from Lexicomp online.
Guenther, L. Sunburn. Canadian Pharmacists Association. Revised February 19, 2019. Retrieved 25May2021 from eCPS.
Valisure. “Valisure Citizen Petition on Benzene in Sunscreen and After-sun Care Products.” Valisure, LLC. Retrieved 24June2021 from https://www.valisure.com/wp-content/uploads/Valisure-Citizen-Petition-on-Benzene-in-Sunscreen-and-After-sun-Care-Products-v9.7.pdf.
DISCLAIMER: The contents of this blog are for educational purposes and are not intended as medical advice. I enjoy researching but the information is general and not comprehensive. Please seek the advice of your healthcare provider (pharmacist/physician etc) with any questions you may have regarding your personal health. Never disregard professional medical advice or delay in seeking it because of something you have read online. Any mention of specific products or personal recommendations are my opinion and not to be taken as medical advice.
