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edited Nov 4, 2017 at 20:54

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So, using a SPF 30 zinc sun blocker blocks equal amounts of UV radiation as a SPF 30 sunscreen. In fact, zinc oxide even is one of the multiple possible active ingredients in a sunscreen, and yes, you are right, it is a physical blocker and therefore better than most sun screens as it protects from UVA and UVB also.

This is where your linked blog and my research conflicts: The using-up of sunscreen has not much to do with sun breaking down zinc oxide, but with the skin braking it down.

I know that a doctor on HuffPost isn't the most reliable claim, but FDA agrees here:

Reapply [sunscreen] at least every two hours, and more often if you’re swimming or sweating.

People should also be aware that no sunscreens are "waterproof.” All sunscreens eventually wash off. Sunscreens labeled "water resistant" are required to be tested according to the required SPF test procedure. The labels are required to state whether the sunscreen remains effective for 40 minutes or 80 minutes when swimming or sweating, and all sunscreens must provide directions on when to reapply.

^{FDA. Sunscreen: How to Help Protect Your Skin from the Sun.}

However, this is the case with chemical sunblockers. Physical sunblockers do not get absorbed as easily by the skin (The swimming and sweating still holds, though):

There are differences between the two main types of sunscreens: physical and chemical. A chemical sunscreen is absorbed by the skin. Sunlight is deactivated or degraded after contact with the organic chemicals contained in the sunscreen. Chemical sunscreens typically contain a range of ingredients like benzones, aminobenzoic acid and cinnamates that, together, protect against UVA and UVB.

A physical block, in contrast, sits on the skin’s surface and contains inorganic compounds like titanium dioxide or zinc oxide that are not absorbed into the skin. In this case, light is either absorbed into sunblock material or reflected away from the skin, similar to a mirror or aluminum foil. Ingredients in physical sunblocks protect against both UVA and UVB and, because they are not absorbed into the skin, they are nonirritating and nonallergenic.

^{Dr. Doris J. Day, What to Look for in a Sunscreen. New York Times. 2009}

Nevertheless, both the FDA and multiple interviews with doctors I have seen encourage patients to use physical sun blockers and re-apply sunscreen every 2 hours.

Remember that sunscreen needs to be reapplied every two hours, or more frequently after swimming, heavy perspiration, or toweling off. Also remember, no matter how much sunscreen you apply, the SPF should be 15 or higher for adequate protection – and ideally 30 or higher for extended time spent outdoors.

^{Elizabeth Kale, Ask The Epxert. Skin Cancer Foundation. 2010}

In addition to sunscreens, sun smart behavior including avoiding the midday sun, staying in the shade when you can, and wearing a hat and sun protective clothing. Use an SPF of 15 or higher, and reapplying it every two hours or more often if you are swimming or sweating, is critical.

^{Dr. Doris J. Day, What to Look for in a Sunscreen. New York Times. 2009}

So, using a SPF 30 zinc sun blocker blocks equal amounts of UV radiation as a SPF 30 sunscreen. In fact, zinc oxide even is one of the multiple possible active ingredients in a sunscreen.

This is where your linked blog and my research conflicts: The using-up of sunscreen has not much to do with sun breaking down zinc oxide, but with the skin braking it down.

I know that a doctor on HuffPost isn't the most reliable claim, but FDA agrees here:

Reapply [sunscreen] at least every two hours, and more often if you’re swimming or sweating.

People should also be aware that no sunscreens are "waterproof.” All sunscreens eventually wash off. Sunscreens labeled "water resistant" are required to be tested according to the required SPF test procedure. The labels are required to state whether the sunscreen remains effective for 40 minutes or 80 minutes when swimming or sweating, and all sunscreens must provide directions on when to reapply.

^{FDA. Sunscreen: How to Help Protect Your Skin from the Sun.}

The FDA agrees:

Reapply [sunscreen] at least every two hours, and more often if you’re swimming or sweating.

People should also be aware that no sunscreens are "waterproof.” All sunscreens eventually wash off. Sunscreens labeled "water resistant" are required to be tested according to the required SPF test procedure. The labels are required to state whether the sunscreen remains effective for 40 minutes or 80 minutes when swimming or sweating, and all sunscreens must provide directions on when to reapply.

^{FDA. Sunscreen: How to Help Protect Your Skin from the Sun.}

However, this is the case with chemical sunblockers. Physical sunblockers do not get absorbed as easily by the skin (The swimming and sweating still holds, though):

There are differences between the two main types of sunscreens: physical and chemical. A chemical sunscreen is absorbed by the skin. Sunlight is deactivated or degraded after contact with the organic chemicals contained in the sunscreen. Chemical sunscreens typically contain a range of ingredients like benzones, aminobenzoic acid and cinnamates that, together, protect against UVA and UVB.

A physical block, in contrast, sits on the skin’s surface and contains inorganic compounds like titanium dioxide or zinc oxide that are not absorbed into the skin. In this case, light is either absorbed into sunblock material or reflected away from the skin, similar to a mirror or aluminum foil. Ingredients in physical sunblocks protect against both UVA and UVB and, because they are not absorbed into the skin, they are nonirritating and nonallergenic.

^{Dr. Doris J. Day, What to Look for in a Sunscreen. New York Times. 2009}

Nevertheless, both the FDA and multiple interviews with doctors I have seen encourage patients to use physical sun blockers and re-apply sunscreen every 2 hours.

Remember that sunscreen needs to be reapplied every two hours, or more frequently after swimming, heavy perspiration, or toweling off. Also remember, no matter how much sunscreen you apply, the SPF should be 15 or higher for adequate protection – and ideally 30 or higher for extended time spent outdoors.

^{Elizabeth Kale, Ask The Epxert. Skin Cancer Foundation. 2010}

In addition to sunscreens, sun smart behavior including avoiding the midday sun, staying in the shade when you can, and wearing a hat and sun protective clothing. Use an SPF of 15 or higher, and reapplying it every two hours or more often if you are swimming or sweating, is critical.

^{Dr. Doris J. Day, What to Look for in a Sunscreen. New York Times. 2009}

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created Nov 4, 2017 at 20:32

Narusan

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TL;DR: No, sunscreen needs to be re-applied every 2 hours

Your product is the same as SPF 30 sunscreen

SPF is a measure of how much solar energy (UV radiation) is required to produce sunburn on protected skin (i.e., in the presence of sunscreen) relative to the amount of solar energy required to produce sunburn on unprotected skin. As the SPF value increases, sunburn protection increases.

^{FDA: Sun Protection Factor (SPF)}

This is irrelevant whether you apply sunscreen with an SPF of 30, or vanilla ice cream with an SPF of 30, or zinc sun block moisturiser with an SPF of 30. The FDA approves all 3 products, and the SPF value is an absolute, standardised value and does not depend on type of product.

So, using a SPF 30 zinc sun blocker blocks equal amounts of UV radiation as a SPF 30 sunscreen. In fact, zinc oxide even is one of the multiple possible active ingredients in a sunscreen.

How long does an SPF 30 sunscreen protect my skin?

“If you’re in the sun, your sunscreen is good for a max of two hours, and depending on the sunscreen it might not even last that long,” Garner says. The skin literally “uses up” the active ingredient in the lotion over time, meaning it can’t do any more.

^{Laura Schoecker. 8 Sunscreen Mistakes You’re Probably Making. HuffingtonPost. 2013}

This is where your linked blog and my research conflicts: The using-up of sunscreen has not much to do with sun breaking down zinc oxide, but with the skin braking it down.

I know that a doctor on HuffPost isn't the most reliable claim, but FDA agrees here:

Reapply [sunscreen] at least every two hours, and more often if you’re swimming or sweating.

People should also be aware that no sunscreens are "waterproof.” All sunscreens eventually wash off. Sunscreens labeled "water resistant" are required to be tested according to the required SPF test procedure. The labels are required to state whether the sunscreen remains effective for 40 minutes or 80 minutes when swimming or sweating, and all sunscreens must provide directions on when to reapply.

^{FDA. Sunscreen: How to Help Protect Your Skin from the Sun.}

Beware of a common misconception

I've read the claim on multiple, reputable websites that SPF multiplies the time you can normally stay in the sun without burns.

Sunscreens provide protection by absorbing, reflecting or scattering the sun's rays. They may also contain chemicals that interact with the skin to protect it from UV rays. Sunscreens are rated according to their effectiveness by the sun protection factor (SPF). A product's SPF number helps determine how long the product will protect you before you need to re-apply it - how long you can stay in the sun without burning. For example, you may normally burn in 20 minutes. If you apply an SPF 15 sunscreen, you'll be protected for about 300 minutes, or five hours (SPF 15 x 20 minutes = 300 minutes). A person with lightly pigmented skin who burns in 10 minutes would be protected for only about two-and-a-half-hours with SPF 15 (SPF 15 x 10 minutes = 150 minutes).

^{American Skin Association. Sun Safety}

According to the FDA, this is a common misconception.

There is a popular misconception that SPF relates to time of solar exposure. For example, many consumers believe that, if they normally get sunburn in one hour, then an SPF 15 sunscreen allows them to stay in the sun 15 hours (i.e., 15 times longer) without getting sunburn. This is not true because SPF is not directly related to time of solar exposure but to amount of solar exposure. Although solar energy amount is related to solar exposure time, there are other factors that impact the amount of solar energy. For example, the intensity of the solar energy impacts the amount.

^{FDA: Sun Protection Factor (SPF)}