What Does SPF Mean? 

SPF stands for Sun Protection Factor.  It measures how much solar energy is needed to cause a sunburn on skin that has sunscreen on it. The SPF value indicates how long it will take the sun's UV rays to cause sunburn, compared to when there is no sunscreen. SPF only describes protection from UV-B rays, which are the sunburn rays that also damage your skin's DNA. UV-A rays penetrate the skin more deeply causing wrinkles and brown.  Because of this, you want to ensure your sunscreen is broad spectrum. This means it protects against UV-A and UV-B rays. Instead of looking for a product with the highest SPF, look for a product with at least an SPF of 30, that is also labeled as broad spectrum, and that you like enough that you will reapply it every 2 hours when out in the sun. 

SPF ratings generally relate to how well a sunscreen protects against UV-B.  The American Academy of Dermatology (AAD) recommends SPF of at least 30 to protect against sunburn and skin cancer.

• SPF 15 sunscreen blocks approximately 93% of UVB radiation.
• SPF 30 sunscreen blocks approximately 97% of UVB radiation.
• SPF 50 sunscreen blocks approximately 98% of UVB radiation

People rarely use as much sunscreen as is recommended or used during testing to reach these SPF claims. Therefore, the AAD recommends a SPF of at least 30. 

What Does PA++ Mean?

PA stands for "Protection Grade of UVA", and is a rating system that measures how well a sunscreen product protects your skin from UVA rays. The higher the PA value, the greater the protection. The PA rating system uses plus signs to indicate the level of UVA protection, with more plus signs indicating higher protection. For example, PA+ offers low protection, PA++ offers moderate protection, PA+++ offers high protection, and PA++++ offers very high protection.

What About Water-Resistance? 

Water-resistant sunscreens are essential when participating in outdoor activities where you are swimming or heavily perspiring because they are formulated and tested to stay on skin when you get wet. However, “water-resistant” doesn't mean “waterproof”, in fact, the FDA no longer allows the term “water-proof” to be used on sunscreen labels. 

The FDA classifies sunscreen as 40 minute or 80 minute water-resistant based on the results of testing.  If a sunscreen lasts longer than 80 minutes in testing all it can be labeled is 80 minutes, that is the highest. Regardless of the classification, you must continue to reapply throughout your time in the sun to keep your skin protected. 

Three Classes of Sunscreen 

There are many ways to classify sunscreens. I am going to do it with the active ingredients that provide the sun protection; you can have chemical, mineral or sunscreens with both.  

Chemical Sunscreen

(azobenzone, octisalate, octocrylene, oxybenzone, octinoxate)

Chemical UV blockers offer UV protection by penetrating into your skin and then absorbing the UV radiation from the sun and converting it into heat.  Recall that the sun emits UV-A radiation, which is associated with photoaging and melanoma, and UV-B radiation, which is more associated with burns, melanoma, basal and squamous cell skin cancers. The most common chemicals available in the US used include azobenzone (absorbs UV-A), octisalate (UV-B), octocrylene (UV-A & UV-B), oxybenzone (UV-A & UV-B), and octinoxate (UV-B). 

Chemical based sunscreens tend to be more cosmetically elegant than mineral based sunscreens because they can be absorbed with minimal residue left on the skin. The downside is that this absorption can lead to unintended consequences.  Most notably, they have possible hormonal effects that could cause changes in our endocrine system.  They are also being increasingly detected in waterways with possible negative consequences to ecosystems and drinking water.  

A study that was published in the JAMA in 2019 showed that when we apply sunscreen to our entire body we absorb more of the active chemical ingredients than we thought AND we don’t know what that means. It does not mean that chemical sunscreens are bad for us, just that our blood levels of the active chemical are higher than we thought or previously identified as safe. We need additional studies to show that even at higher levels, these chemicals are still safe. The FDA has asked sunscreen companies to do this and those studies are going on now. 

Physical or Mineral:

(zinc and titanium)

These work by creating a physical barrier on the skin's surface to reflect and scatter UV radiation from the sun as well as absorbing UV.  The main minerals used for this are zinc oxide and titanium dioxide.  Mineral sunscreens are considered non-toxic and have the advantage of well-documented safety and effectiveness.  They are the only sunscreen ingredients in the United States labeled as Generally Recognized As Safe (GRAS).  They are also more photostable, meaning they remain effective longer when exposed to sunlight unlike many chemical sunscreens, which start to break down as soon as they are exposed to UV.  They still need to be reapplied every two hours.  

Generally considered to be gentle on the skin, they are less likely to cause irritation or allergic reactions compared to chemical sunscreens. They are also less likely to cause irritation or allergy than chemical UV blockers making them more for sensitive skin and children.  Zinc in higher percentages (over 10%) offers broad spectrum protection against both UVA and UVB.  Titanium provides UVB protection.  Made from naturally occuring minerals, physical sunscreens are more environmentally friendly. The downside is they can be less cosmetically elegant by leaving a white residue on the skin and contributing to block pores.  

Combination

These contain both chemical and physical blockers that have historically be called out in the active ingredient list. But there is a newer category of these sunscreens in the US that feature zinc oxide as a key ingredient, claim 100% mineral but include chemical UV blockers as well. These are included to reach a higher SPF claim and make the zinc more spreadable.  Historically, both types of UV blockers (chemical and physical) were highlighted on the active ingredient list, but more recently, this somewhat controversial step of sunscreen "doping" is happening where chemicals are being included in mineral sunscreens that are nearly identical to the regulated chemical filters but are not being disclosed because they are not regulated in the US. Ingredients to look for include butyloctyl salicylate (nearly identical to octisalate), ethyl ferulate (similar to octocrylene), diethylhexyl syringylidenemalonate (octinoxate) and tridecyl salicylate (octisalate). The take home point is when you are trying to avoid chemical sunscreens, look out for these ingredients even if the sunscreen says 100% mineral sunscreen. 

What is Organic vs Inorganic Sunscreen?

A definition of organic is “of, relation to carbon compounds” which when applied to sunscreen means carbon-based chemicals are used to protect the skin from UV radiation. Here, the chemical sunscreen ingredients are technically considered organic as in “organic chemistry” and are a chemical with a carbon backbone (oxybenzone, avobenzone, and octinoxate) instead of mineral or physical or inorganic sunscreens made from zinc and titanium which do not contain carbon.   

What Does Reef-Safe mean? 

Reef safe is a non-regulated term referring to sunscreens without oxybenzone and octinoxate.

When to Apply Sunscreen?

Apply sunscreen every morning. You still need to use an antioxidant serum with vitamin C and moisturizer (if you have dry skin) before you apply your sunscreen and makeup after. There are some great sunscreen options with tint in them that can also work like make up to blend the skin.

If you are going to be outside, you need to apply sunscreen to all exposed areas every two hours. This can be difficult, so I always recommend hats, sunglasses, sun protective clothing and seeking shade during the hottest hours of the day. 

What About Vitamins in Sunscreen?

Yes, sunscreen that is formulated with vitamins is fine but don’t count on your antioxidants in your sunscreen as your only form of vitamins for your skin. Since zinc sits on the top of the skin and is a large molecule, very little from the sunscreen will actually be absorbed. I always put my antioxidant serum with Vitamin C+E on bare skin first.  Another ingredient people often ask about is retinyl palmitate, a form of Vitamin A. Reports that retinyl palmitate is not a safe ingredient are based on a study from nearly 20 years ago that has never been reproduced or studied when it serves as an ingredient in sunscreen. In addition, there is no scientific evidence that retinyl palmitate is a carcinogen in humans. In fact, retinyl palmitate is found in our skin, where it works as an antioxidant. It is often included in sunscreen as a preservative.

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Meet the author: Board-certified and practicing dermatologist, Dr. Heather D. Rogers, MD, is the founder of Doctor Rogers Skin Care and Modern Dermatology in Seattle, Washington. She studied at Stanford, University of Washington School of Medicine and Columbia University Medical Center. She lectures nationally, is well published, and an active member of the American Academy of Dermatology. Highly respected among the skin care community, Dr. Rogers has been annually named “Top 1% of Most Honored Doctors in the US” by Castle Connolly.