Your Top 15 Sunscreen Questions Answered

In this article:
Is it safe to use homemade sunscreen?
Does sunscreen expire?
Can you use expired sunscreen?
Does sunscreen go bad after sitting in the sun?
Does sunscreen prevent tanning?
Do you need sunscreen if you have sun protection clothing?
What is UPF and how does it differ from SPF?
How does sunscreen work?
How long does sunscreen last?
Is SPF 30 enough?
When was sunscreen invented?
Does sunscreen block vitamin D?
When can a baby use sunscreen?
Can sunscreen cause acne?
Is sunscreen safe?

Does sunscreen go bad? What does SPF even mean? Can DIY homemade sunscreen adequately protect skin? What’s the deal with sun protective clothing? Is sunscreen even safe?

We’ve vetted your top sunscreen questions against the research and medical experts to ensure you’re protected and armed with the truth about sun safety.

Is it safe to use homemade sunscreen?

Applying natural oils such as carrot, raspberry and coconut, which have been touted online as natural sunscreen oils, or slathering on DIY sunscreen featuring home-mixed zinc oxide, can leave skin susceptible to sun damage.

These oils and at-home concoctions simply don’t make the grade when it comes to robust sun defense. The American Academy of Dermatology (AAD) and the Skin Cancer Foundation have explicit warnings about making natural sunscreen at home due to the risks associated. The AAD says, “homemade sunscreens do not go through the rigorous testing required of commercial sunscreens by the U.S. Food and Drug Administration (FDA), which means that their Sun Protection Factor (SPF), water resistance and shelf-life cannot be guaranteed” (1). The Skin Cancer Foundation adds, “Even if you do include effective UV filters [in your homemade DIY sunscreens] like zinc oxide, it’s impossible to create a product with the level of precision required to guarantee effective, long-lasting protection” (2).

Beyond this, an independent study of dermatologists in the United Kingdom tried 15 different online homemade sunscreen formulas and found that three of the “recipes” didn’t even contain any sunscreen ingredients and “the other 12 cannot be considered as sun protection products since all of them have an SPF under 6, the threshold value required in Europe” (3).

In the end, it’s simply not a risk worth taking, especially when skin health and safety are on the line.

Does sunscreen expire?

Sunscreen does indeed expire. To ensure safety and efficacy, the United States Food and Drug Administration (USFDA) requires sunscreen products to list an expiration date, which can usually be found stamped on the packaging or imprinted along the crimp portion of tube-packaged SPF products.

However, there is one exception to this rule: If the manufacturer has proven that their sunscreen will remain stable for at least three years via stability testing, the product doesn’t have to be stamped with an expiration date. In that case, the FDA warns that the product “should be considered expired three years after purchase” (4). We’d even go one step further to say that once you open the product, it’s a smart idea to use it up before the PAO (period after opening) date, which is usually 12 months for cream/lotion sunscreens.

Note: Sunscreens sold outside of the United States may be subject to different expiration policies, so it is important to read and understand the label to ensure you’re getting reliable protection.

Can you use expired sunscreen?

Expired sunscreen should not be relied on to protect your skin, as there is no assurance that the product will be fully effective. While you might still get some protection, there’s no way to know exactly how much. Using insufficient sunscreen can lead to sunburnt skin, as well as UV damage that harms skin in the long run, while also accelerating visible signs of aging. Most importantly, insufficient protection can increase the risk of skin cancer.

Does sunscreen go bad after sitting in the sun?

Leaving your sunscreen out in the direct sun for an extended period of time can have a negative effect on the formula’s stability. To keep your SPF in tip-top condition, especially on beach days, the FDA recommends protecting your sunscreen by wrapping it in a towel or storing it in the shade or a cooler. (4)

Does sunscreen prevent tanning?

A well-formulated sunscreen will prevent tanning or the deepening of skin’s color as it works to shield skin from the harmful rays responsible for triggering that response. However, research shows that user error in under-applying sunscreen is still prevalent both in the United States, as well as many other countries, which could mean you may still see a tanning effect or sunburn on skin even after applying SPF (5). One of the biggest mistakes that most people make is not applying/reapplying sunscreen liberally enough to achieve adequate protection.

It's also important to point out that sunscreen does not protect us from 100% of UVA and UVB rays. This gives you even more reason to couple sunscreen use with other sun smart behaviors, such as seeking shade when possible and wearing sun-protective clothing, especially on days when you’ll be exposed to the sun for longer periods of time. Speaking of which…

Do you need sunscreen if you have sun protection clothing?

Sun protection clothing from reputable brands will shield against both UVA and UVB rays in the areas of skin that it covers, so no sunscreen is necessary underneath the clothed area. However, any areas of skin that are left exposed to the sun still need sunscreen. Similar to sunscreen, you want to look for clothing rated with a UPF (ultraviolet protection factor) of 30 or higher (6).

What is UPF and how does it differ from SPF?

UPF is the rating system used to identify the level of protection clothing provides against both UVA and UVB rays. This is different from a sunscreen’s SPF rating, which only signifies effectiveness against UVB rays. To ensure UVA protection, your sunscreen must be labeled as “broad spectrum” which signifies the presence of sunscreen ingredients that also protect against UVA wavelengths.

Wait, SPF doesn’t measure UVA rays—what’s up with that?! Let’s delve into how sunscreens work in a bit more detail…

How does sunscreen work?

Sunscreen actives work in skin's uppermost layers to both absorb and, to a lesser extent, deflect and scatter the sun’s harmful rays. Think of them as shield for your skin—while not completely failproof, they do a good job of hindering damage to skin from the sun to the extent possible.

As mentioned earlier, SPF is a rating system that measures how much UVB protection a product delivers when applied evenly and liberally. UVB rays are the rays that trigger sunburn and other visible changes to skin’s surface, including discolorations. UVB radiation also plays a role in skin cancers. Its intensity wavers depending on your geographic location, altitude, time of day, and level of cloud cover (but make no mistake, clouds still let harmful UV light through).

UVA rays are an even bigger threat because a much larger percentage of them reach earth’s surface and hence, our skin. UVA rays are present at the same intensity all day long. They penetrate further into skin than UVB rays, steadily destroying key substances that give skin its youthful, healthy appearance. Moreover, UVA rays are a major contributor to every type of skin cancer. Remember, your sunscreen must be labeled “broad spectrum” to ensure it protects against UVA rays…the SPF number itself doesn’t tell you that.

Note: Sunscreens in Asia and some other parts of the world are labeled with a PA+ rating (Protection of UVA), which is a measurement of UVA protection. This rating isn’t widely used for US-based sunscreens.

How long does sunscreen last?

Once you’ve applied your sunscreen, how long it will last (protect your skin) depends on several factors. The general recommendation is to reapply every two hours.

In the past, it was thought that if you knew how long it takes your skin to turn pink or begin to darken when exposed to the sun without sunscreen, then you could take that amount of time in minutes and multiply it by the SPF number on the bottle to determine how long it will protect your skin. However, SPF ratings aren’t just about time, they’re also about the intensity of UVB based on your location, amount of cloud cover, latitude, season, and proximity to reflective surfaces like water, snow, and sand.

Additionally, you must consider whether you’re sweating, swimming, or doing anything else that might dilute or rub off your sunscreen.

Complicated, right? That’s why the two-hour reapplication rule tends to stick, even though it oversimplifies things.

What if you’re indoors for almost the entire day, and not sitting near a window? If your sunscreen isn’t being broken down by UV rays and you’re not perspiring heavily, the two-hour reapplication rule isn’t necessary.

Is SPF 30 enough?

Medical organizations around the world recommend broad spectrum SPF 30 or greater for daily use (7). While that may be enough for most people in their regular day to day lives, whether SPF 30 will be enough for you comes down to how much exposure you’re likely to get and your overall health.

If you’re outside in direct sunlight or if the UV index (the measure of sun’s intensity) is 8 or above, that’s going to have a different impact than spending the entire day indoors at the office or spending time outside when the sun’s less intense. For days that you know you’ll be more exposed, or the UV index will be higher, reaching for SPF 50 isn’t a bad idea. Don't forget a broad-brimmed hat and sunglasses, too.

People with increased risk factors should always follow the SPF recommendation of their doctor or dermatologist.

When was sunscreen invented?

While previous civilizations used various measures to limit sun exposure, research points to 1928 as the first documented use of a sunscreen emulsion in the United States, which used UVB filters to protect against sunburn (8). However, there’s a bit of debate among historians about who actually invented the first commercialized sunscreen. That aside, we do know development of specifications for sun protection factors didn’t occur until 1974, and in 1980 the first documented sunscreen with UVA filters was released (9). In the decades since then, sunscreen formulations have improved leaps and bounds in terms of aesthetics, efficacy, and options for all skin types and skin tones.

Does sunscreen block vitamin D?

While it’s true that sunscreen inhibits exposure to UVB rays that trigger vitamin D production in skin, research shows foregoing sunscreen in order to get more vitamin D is not the answer (10). Sunscreen’s effect on vitamin D levels is considered minimal for most people, and ironically, skipping sunscreen and getting a tan can inhibit vitamin D in its own way. What we know to be unequivocally true is that exposing your skin to harmful UV rays has serious repercussions.

If you’re concerned about vitamin D deficiency, there are far more effective ways to get this nutrient, which your doctor can discuss with you. Board-certified dermatologist Dr. Joyce Park adds, “Vitamin D is also easily obtained through your diet, through fortified dairy products, egg yolks, cheese, seafood, and more.”

When can a baby use sunscreen?

For babies under 6 months, the American Academy of Pediatrics recommends sun protective clothing and seeking shade when possible. When sun avoidance isn’t an option, using mineral based (zinc oxide or titanium dioxide) sunscreen on exposed areas of skin such as the face and hands is recommended (11). For babies 6 months and older, regular sunscreen application is advised. As always, consult your child’s pediatrician and follow their advice.

“Never spray sunscreen onto your child’s face directly due to inhalation risk; instead, spray the sunscreen onto your hands and pat onto the child’s face,” cautions Dr. Park.

Can sunscreen cause acne?

Sunscreen in and of itself does not cause acne, but if the formula you use has a thick, heavy, pore-clogging consistency or if you don’t wash it off properly at night, there’s a chance you could break out from it.

For blemish-prone skin, lighter weight, non-greasy, fluid sunscreen formulas are a great sunscreen option. At night, remove the sunscreen with a gentle yet thorough cleanser.

Is sunscreen safe?

While the safety of sunscreen has been called into question by media headlines in recent years, the FDA and American Academy of Dermatology still strongly agree that wearing sunscreen is safe and plays a key role in protecting your skin (12). Scientific studies support this as well, and most notably, research shows sunscreen use reduces the risk of skin cancer (13).

Some of the concern around sunscreen use was heightened in September of 2021 when the FDA announced that they would be taking steps “aimed at improving quality, safety and efficacy of sunscreens,” including analyzing more data on certain UV filters (14). It’s important to point out that this doesn’t mean those ingredients are unsafe, nor has the FDA issued a warning to stop using them or advised formulators to avoid them.

If you have additional questions about the safety of your sunscreen, a board-certified dermatologist can help.

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References for this information:

1. American Academy of Dermatology, Website, Accessed February 2025
2. The Skin Cancer Foundation, Website, Accessed February 2025
3. Journal of Cosmetic Dermatology, June 2021, pages 1,788-1,794
4. FDA.gov, November 2021, ePublication
5. Journal of the European Academy of Dermatology and Venereology, November 2019, pages 1,112–1,117
6. Photodermatology, Photoimmunology, and Photomedicine, January 2022, pages 1-11
7. Australian and New Zealand Journal of Public Health, 2019, ePublication
8. Saudi Pharmaceutical Journal, November 2019, pages 1,009-1,018
9. Journal of Cosmetic Dermatology, April 2021, pages 1,044-1,049
10. Journal of Korean Medical Science, March 2020, pages 1-11
11. American Academy of Pediatrics, July 2021, ePublication
12. American Academy of Dermatology Association, April 2022, ePublication
13. Cosmetics, July 2019, pages 1-13
14. FDA.gov, September 2021, ePublication