Sunscreen: Basics and Beyond

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Sunscreen is extremely important to our skin health and appearance. UV light is responsible for about 80% of skin aging, which includes skin discoloration, hyperpigmentation (dark spots), leathering, and wrinkles and fine lines. UV exposure also causes DNA damage in skin cells, which may lead to cancer. Additionally, sun exposure will exacerbate skin conditions such as melasma. Sunscreen protects against both photo-aging (sun-related aging) and cancer, blocking up to 99% of all UV rays. Since summer is around the corner, I thought tackling some of the basics about sunscreen would be appropriate. This is a longer post with lots of details that I hope readers will find helpful. Summary and product recommendations are at the end of the post. 


  • For effective protection against skin cancer and photo-aging, wear sunscreen everyday, year-round, rain or shine.
  • Apply 1 tsp of sunscreen to cover your face, neck and chest to get adequate protection (and don’t forget your ears, hands, and other exposed body parts with additional sunscreen).
  • Reapply every 2 hours when exposed to sunlight.

For more a general skincare guide that goes beyond sunscreen, click here.

If you liked this article, visit my blog Inert Perfection for more like it!


The sun produces several kinds of light, most of which will reach us through the Earth’s atmosphere and will affect our skin in different ways. The most important ones are ultraviolet A and B (UVA, UVB), visible, and infrared light.

We have the most amount of research on ultraviolet light. UVB light has a short wavelength, which means it can’t penetrate the skin very deeply and in fact, most of its effects are confined to the top layers of the skin. UVB causes sunburns and redness on the skin and is responsible for tanning as well. It will also damage skin cell DNA on the skin surface, causing cancer. UVB is strongest in the summer and midday, between 10 AM and 4 PM. It is blocked effectively, however, by clouds and glass windows. UVA, on the other hand, has a long wavelength and penetrates deeper, into the dermis layer of the skin. There are two kinds of UVA: UVA1 and UVA2. They both damage collagen, suppress the skin immune system, cause skin cancer, and are responsible for most of the photo-aging we experience. UVA is known as the “silent killer” because it does not burn the skin and we can’t feel or see it. Unlike UVB, UVA retains its strength all year round and throughout the day. It penetrates cloud cover and 62.8% of UVA will penetrate through glass windows. UVA also bounces off reflective surfaces such as water. UVA is the reason why we should wear sunscreen every single day. 

Visible light is light we can see – for example, blue light emitting from illuminated screens and light bulbs. While visible light is not known to cause skin cancer or wrinkles, it will drive hyperpigmentation and melasma. Visible light can also be beneficial to the skin. Blue light therapy can be used to treat acne as well as prevent skin cancers. Red light therapy can be used to treat fine lines and stimulate collagen production.

We feel infrared light as heat. We have very little data on this light’s effect on skin, so there is no information out there yet as to whether or not it causes cancer or aging. There are no sunscreens that protect against infrared light – only protective clothing and a wide-brimmed hat will provide that.


Sunscreen protection comes in two forms: chemical and physical. Chemical sunscreens contain filters that work by absorbing UV rays and converting them into harmless energy on the surface of the skin. There are many different kinds of filters used for this purpose, some of which are not yet approved by the FDA, but are widely available outside the U.S. Each filter differs in how well it protects from UVA1, UVA2, and/or UVB, how long it remains effective, and how much it degrades in the presence of UV light (photo-stability). Chemical sunscreens usually combine multiple filters in order to cover the full spectrum of UV light. Most chemical sunscreens degrade with time, so it’s best to replace them within 3 years.

Chemical sunscreens require at least 20 minutes to absorb properly and create a film on the skin that protects against UV light. Therefore, wait 20 minutes before sun exposure after applying a chemical sunscreen. They are usually more cosmetically elegant than physical sunscreens in that they don’t leave a white cast and absorb quickly and well. However, they are more likely to cause skin irritation and allergic reactions.

Physical sunscreens contain the minerals Titanium Dioxide and/or Zinc Oxide. These minerals work by deflecting UV rays from the skin, providing a physical blocker. Zinc Oxide will block the full spectrum of UVA1, UVA2, and UVB while Titanium Dioxide only blocks UVA2 and UVB. Both minerals will also provide some protection against visible light. They are both photo-stable, although Zinc Oxide will degrade slowly in the presence of UV light. Physical sunscreens will protect against UV and visible light immediately when applied.

Dermatologists in the U.S. say that the percentage of Zinc Oxide and Titanium Dioxide in a product doesn’t matter and the most important thing is the SPF rating. However, there are some skincare chemists who say that you need at least 5% Zinc Oxide (and ideally between 10-20%) or 5% Titanium Dioxide for the sunscreen to be effective. Since there is conflicting information on this, I choose the safer course of having a physical sunscreen with 5% or higher active ingredients.

There are many combination sunscreens that include both physical blockers and chemical filters. These provide good photo-stability and protection while offering smoother application and more comfortable wear.


How can we tell how effective a sunscreen is in protecting us against UV damage? The standardized form of evaluating UVB protection is the Sun Protection Factor or SPF. An SPF of 15 means that the particular sunscreen will protect against approximately 93% of UVB rays. SPF 30 protects against 97%, SPF 50 against 98%, and SPF 100 against 99%. The downside to purchasing very high SPF sunscreen is, of course, the price tag. You need to decide for yourself whether the extra protection is worth the price. Personally, I don’t purchase sunscreens with SPF ratings over 50.

In the United States and many European countries, a label of “broad spectrum” indicates that the sunscreen also protects against UVA. However, there is nothing to show how effective or for how long the protection is. In East Asian countries, UVA protection is measured by a “PA” rating. This ranges from PA+ to PA++++, the former being little protection against UVA and the latter very strong protection.

Sunscreen is regulated as a drug in the United States by the FDA. As such, it must follow strict guidelines when it comes to labeling. When a sunscreen claims that it is water resistant, it must have demonstrated through rigorous trials that the touted SPF will remain intact while swimming or sweating for the amount of time written on the packaging. For example, a product claiming to be 40 minutes water resistant and to have an SPF of 50 means that it will protect you against 98% of UVB rays for 40 minutes while you are immersed in water.


Now that you know what to look for in a sunscreen, the next step is to establish a habit of daily application. This is the most important part of the process because no matter how effective the sunscreen, it won’t work if you don’t apply it properly!

Most people fail to apply adequate amounts of sunscreen. In order to reach the SPF rating of a particular sunscreen, you must apply 2 mg of sunscreen per square centimeter of exposed skin. As a general guideline, for the average body size, you need about 1/4 teaspoon for your face alone or 1 teaspoon for face, neck and chest. Additionally, you need 1 teaspoon for each arm, 2 teaspoons for the front and back torsos, and 2 teaspoons for each leg. For an even broader guideline, that is about 1 shot glass full of sunscreen from head to toe. As an example of how much the amount of sunscreen impacts protection, the average amount of SPF 50 sunscreen a person applies to the face will only provide 33% UVB protection compared to the 98% it is supposed to give.

Reapplication is also very important. If you are directly exposed to sunlight, either outdoors or through a glass window, reapply sunscreen every 2 hours. If you are sweating profusely, swimming, or wiping yourself off, you need to reapply immediately unless the sunscreen is water resistant. If you are indoors for most of the day with only brief sun exposure, you can reapply less often. A chemical sunscreen will need to be reapplied about twice to three times a day because it is often photo-unstable and degrades with time. A physical sunscreen won’t need to be reapplied unless you are sweating or touching or wiping your skin.

Sunscreen should be the last step in your skincare routine. The efficacy of sunscreen will decrease with products layered on top of it. You should wait for your moisturizer to dry completely (about 3-5 minutes) before applying your sunscreen. Likewise, you should wait for your sunscreen to dry completely before applying makeup so as to not dilute the sunscreen or cause uneven coverage.

The best kind of sunscreen to use is a lotion or cream. Sprays and powders contain larger molecules that won’t distribute sunscreen evenly on the skin. In addition, both are difficult to use in adequate amounts. Makeup containing SPF is also not a good standalone sunscreen because the amount you need to provide good sun protection will make you look ridiculous.

A nice trick for those who don’t use much makeup is to use one thinner layer (1/8 teaspoon) of physical sunscreen and then another layer (1/8 teaspoon) of tinted sunscreen on the face. This will give you the amount of protection you need without giving more coverage than you are comfortable with. As an added bonus, most tinted sunscreens contain iron oxides, which will provide extra protection against visible light. You may simply use only tinted sunscreen, but I personally have found this to take much more time to dry down on my skin. Finally, you shouldn’t mix sunscreens with Avobenzone and those with Titanium Dioxide. Avobenzone is a commonly-used UVA filter in the U.S. and Titanium Dioxide is known to accelerate its degradation and make it less effective.


I am unable to recommend many face sunscreens because I have not started applying sunscreen regularly until recently. I also do not wear face makeup except BB cream occasionally on my T-Zone, so I do not know how well any sunscreen sits under makeup. I personally prefer pure physical sunscreens, so I can comment very little on chemical ones. However, I am currently experimenting with new sunscreens, so I will have an updated list in the future. For body sunscreens, I just use good ol’ Neutrogena.

Click on the sunscreen names below to go to the product page.

1.)  Biore UV Aqua Rich Watery Essence (Japanese)

This is a purely chemical sunscreen with ethylhexyl methoxycinnamate (Octinoxate – UVB absorption, photo-unstable) and bisethylhexyloxyphenol methoxyphenyl triazine (Tinsorb S – not available in the U.S. Photostable; UVA1, UVA2, and UVB absorption) as the active ingredients. This sunscreen is best for normal to oily skin types. It contains a large amount of alcohol, which helps with product absorption but will also dry out your skin. This smells strongly of alcohol but the smell dissipates quickly after application. I love this sunscreen in the summer because it absorbs very quickly and doesn’t leave anything behind. It is SPF 50+ with a PA++++. It is also water resistant, but because it is not regulated by the FDA, does not say how long it will remain so.

2.) EltaMD UV Physical Broad Spectrum SPF 41

This is an all-physical sunscreen that is water resistant for 40 minutes. It contains 9% Zinc Oxide and 7% Titanium Dioxide as well as iron oxides. It is slightly tinted and provides light coverage. It may not be appropriate for darker skin tones. It takes about 10 minutes to dry down completely and not feel sticky or heavy.  I would recommend this for normal to oily skin types as it did dry me out a little in the winter. I found it to have a mattifying effect in my T-Zone. This is also a good option for sensitive skin types as it is fragrance free. If you have an allergy to iron oxides, you should avoid this sunscreen.

3.) Make P:rem UV Defense Me Blue Ray Sun Cream (Korean)

This is my favorite physical sunscreen so far because the application is so smooth. It contains both Zinc Oxide and Titanium Dioxide and has SPF 50+ and PA++++. It absorbs very quickly and leaves a slightly dewy finish without a white cast (I have fair skin with yellow undertones). This is a great sunscreen for normal to dry skin types as it is moisturizing. The texture is slightly thicker, but feels light-weight on the skin. This does not contain any synthetic fragrances, but does have some plant oils that produce a light citrus scent. Note: the citrus oils in this are not cold pressed and will not cause photo-toxicity.

4.) Australian Gold Botanical Sunscreen Tinted Face Mineral Lotion

This is a purely physical, tinted sunscreen with 4% Zinc Oxide, 4% Titanium Dioxide, and iron oxides. It is broad spectrum SPF 50 and water resistant for 80 minutes. It is fragrance free. Again, if you have an allergy to iron oxides, please avoid. (Halley Opinion: I recently started using this sunscreen and have been really liking it. It is slightly tinted, but the coverage is fairly transparent. The texture feels like a mousse and spreads easily and leaves a matte finish on the face. Despite the second ingredient being shea butter, the product is not greasy and feels very light when applied. I have not had any adverse reactions such as clogged pores or break outs. So far I’ve been quite impressed and also love the very reasonable price point.)


  • Visible light (e.g. light from cell phones, computers, light bulbs, etc) causes brown spots and melasma, but can also be used under certain conditions to treat acne, cancer, and stimulate collagen production.
  • UVB causes sunburns, tanning, some aging, and cancer. It is strongest between 10 AM and 4 PM and in the summer.
  • UVA causes wrinkles, brown spots, melasma, skin texture problems, and cancer. It is the same strength all year round and throughout the day. It will penetrate through clouds and glass windows.
  • Chemical sunscreens absorb UVA and UVB light and convert them into heat. You must wait 20 minutes after applying these before sun exposure. These are more likely to cause skin irritation, but absorb better and more quickly and feel better on the skin than physical sunscreens.
  • Physical/mineral sunscreens deflect UVA, UVB, and some visible light. These will work immediately upon application. Many, but not all, formulations will leave a white cast and will feel heavier on the skin.
  • Use a broad spectrum, SPF 30 or above sunscreen to provide adequate protection against both UVA and UVB. If purchasing products from Asian countries, look for PA+++ or PA++++ and SPF 30 or above.
  • Water resistant sunscreen will maintain the SPF coverage for 40 or 80 minutes while you are swimming or sweating.
  • Apply 1/4 tsp sunscreen to your face; 1 tsp to face, neck and chest; or 1 shot glass full for face and body. This is necessary to obtain the amount of protection indicated by the SPF and PA ratings.
  • Reapply every 2 hours if directly exposed to sunlight, either outdoors or through glass windows. If you wipe your skin, sweat, or are swimming, reapply immediately unless the sunscreen is water resistant.
  • Reapply 2-3 times a day if you are minimally exposed to the sun and using chemical sunscreen. If using physical sunscreen, there is no need to reapply with minimal sun exposure unless you are sweating or touching or wiping your skin.
  • Apply sunscreen as your last skincare step. Wait 3-5 minutes for it to dry completely before applying makeup to retain strength and even coverage.
  • Lotions and creams are preferable to sprays and powders for efficacy.

Disclaimer: I am not a dermatologist, esthetician, or skincare chemist. I am merely someone who is deeply interested in skincare and do a lot of research on the topic. I highly encourage you to do your own research and not rely on my word alone. Please be cognizant that the best skincare is one suited for your skin type. I have normal to slightly dry skin, so the products I use may not be appropriate for you if your skin type differs from mine.


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