Since the use of sunscreens has been on the rise, they have gained many advocates as well as many opponents. Opponents of sunscreens claim that they block the synthesis of vitamin D, which is essential for our health. There are also extreme opponents who claim that using sunscreens is more harmful than unprotected sun exposure. However, is it true that sunscreens block vitamin D synthesis?

Basic information on vitamin D

Vitamin D acts as a hormone in the body and is synthetized by UV light. Vitamin D comes in two forms (D₂, D₃). Vitamin D₂ is obtained from plant nutrition and oral supplements. Vitamin D₃ is mainly obtained by exposing the skin to ultraviolet B (UVB) radiation in sunlight and consuming foods such as oily fish. Vitamin D₂ and D₃ are metabolised in the liver and kidney to 1,25-dihydroxyvitamin D or calcitriol, which is a biologically active form. Calcitriol plays an important role in regulating the metabolism of calcium, phosphate for maintaining metabolic functions and for skeletal health.

How can one get vitamin D?

Vitamin D is also found in mushrooms, wheat germ oil, egg yolk, liver and fish oil. Vitamin D content in most foods ranges from 50 to 200 units per serving. Therefore, food cannot provide enough vitamin D, which is why most people synthetize it after sun exposure. Sun-induced vitamin D synthesis is strongly influenced by season, time of day, latitude, altitude, air pollution, skin pigmentation, use of sunscreens, passage through glass and plastic, and age.

Interesting fact: Even when older people are regularly exposed to sunlight, they produce 75% less vitamin D3 than young people.

Inadequate vitamin D intake can lead to postmenopausal osteoporosis and reduced bone density. Low vitamin D intake is also associated with heart and vascular diseases, depression, dementia and other conditions.

How is vitamin D synthesized after sun exposure?

Vitamin D3 can be produced in the skin when exposed to ultraviolet radiation B (UVB), so it is possible to increase vitamin D3 levels by exposure to UVB rays. During exposure to sunlight, radiation with a wavelength of 290–315 nm penetrates the skin. Most of this UVB radiation is absorbed in the epidermis, so when exposed to sunlight, most of the vitamin D3 is produced in the skin, in the living cells of the epidermis.

A quick recap on UV radiation

As we already know, exposure to UV radiation is not safe. Namely, we divide the UV spectrum into ozone-retained UVC rays, UVB rays that cause sunburns, UVA rays that cause photoaging. Unnecessarily prolonged exposure to UV light without protection can lead to skin cancer. For a reason, sunscreens have been developed to protect us from the harmful effects of UV radiation. Sun creams are designed to absorb and partially repel UVB radiation.

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If sunscreen blocks UVB rays does it block vitamin D synthesis as well?

Well, here we are. Where scientists from different disciplines are arguing with each other. Last time, I heard from a colleague that one dermatologist claimed that reduced vitamin D synthesis from sunscreens is more harmful than unprotected sun exposure. To put it mildly, I was almost hit by a stroke, but let’s go down the line. Sunscreen with sun protection factor (SPF) 30 absorbs approximately 96% of UVB radiation. So, by adding 2 + 2, topical application of sunscreen with SPF 30 reduces the skin’s ability to produce vitamin D3 by the same amount, ie 96%.

In principle, we calculated that only 4% of UVB radiation can access our skin with SPF 30, which is a very low chance for vitamin D synthesis, right? But this is where  you need to ask yourself how much sunscreen you really apply to your skin. In order to achieve the protection stated on the packaging – so in our case SPF 30 we need to apply 2mg / cm2 of skin. For the whole face, this means two full fingers of the cream.

A short calculation to back up my claims

The average surface area of ​​all skin in an adult is 1.5-2.0 m². So if we need to apply 2mg / cm² the calculation is as follows.

The result is 32 g per coat. Therefore, 1/3 of the entire 100 ml tube of sunscreen should be used to properly protect the entire body. Of course, we did not take into account that the sunscreen should be reapplied every 2 hours.

Let’s be real, we apply such a small amount of sunscreen to the body that the question is if we have an SPF protection factor of 5. So with SPF 5, we are about 70% protected against UVB radiation. This may sound like a lot, but this time it can pass as much as 30% of UVB radiation to the skin! Not to mention some body parts that are not usually protected at all. Or maybe we are in the shade and don’t put sunscreen on because the UVB rays can’t reach us. All of these unprotected parts allow 100% passage of UVB radiation and thus synthesis of Vitamin D, but also increased chances of skin cancer.

UVA protection is beneficial for Vitamin D

A number of studies investigating the influence of sunscreen on vitamin D synthesis have found that the use of sunscreen is likely to have minimal impact on vitamin D. UVA rays have no effect on vitamin D synthesis, although one in vitro study showed that UVA2 (315–340 nm) can cause vitamin D to break down, in which case protection against UVA may be beneficial for vitamin D production.

Controlled field studies with true sun exposure are the best way to determine the effect of sunscreen on vitamin D synthesis. The results of such studies report that no change in serum 25 (OH) D3 vitamin concentration occurs despite the use of sunscreen.

In fact, most studies published to date have shown no association between the use of sunscreens and vitamin D deficiency, nor with regular use of SPF> 15. In general, other protective methods (eg, shading, wearing protective clothing and long sleeves) ) affect vitamin D status more than using sunscreens.

UV radiation is more dangerous than sunscreens

Daily skin protection is recommended for all skin phototypes. This includes staying in the shade, wearing headgear and clothing, wearing sunglasses, and applying broad-spectrum sunscreen. These strategies will help prevent sunburn and skin cancer. The use of sunscreen for daily sun protection does not compromise the synthesis of skin vitamin D synthesis, even when the sunscreen is used in the predicted amounts (2mg / cm2). Increasing UVA-PF in sunscreens, however, even improves vitamin D3 production.

In case of reduced vitamin D level, this should be replaced. Oral supplementation is easy and does not pose significant risks. The risk-benefit calculation shows that, instead of sunbathing, it is better to take nutritional supplements with this vitamin to increase vitamin D3 levels.

Nanoparticles are one of the latest threats to humankind. Almost. Certainly not in cosmetics. Nanoparticles don’t exist from yesterday, they have been here for quite some time. Only science, that studies them – nanotechnology is relatively new.

What are nanoparticles?

Nanoparticles are small units of material, that is smaller than 100nm. We know that nanometer is 10⁻⁹ right? Nanoparticles can come from a different origin: natural (desert dust), unintentionally produced (burning out biomass and fossil fuel), engineer (sunscreens and other cosmetics, textile).

Photography: Neja Stojnić

Why do we even use nanoparticles?

Nanoparticles exhibit new properties and functions of already known materials. This properties are very different than the properties from the same ingredients, but bigger order of size. Not only in cosmetics, but also in food technology and medicine they show a lot of advantages.

  • they stabilize and protect ingredients and extend the time of usage (fatty acids in oil, vitamins and antioxidants)
  • they affect  solubility and speed of solution of the ingredients
  • better activity on the skin
  • higher effectiveness and tolerance of UV filters
  • delivering cosmetic active ingredients in deeper layers of the skin

But everyone says, that nanoparticles are bad,..

Every good invention has a bad side, right? Nanoparticles can be toxic. Toxicity can be a consequence of damaging effects of decomposed products from nanoparticles. Physical properties of nano sized particles (big surface, charge), regardless the chemism of the products that compose nanoparticles, can be a reason for toxicity as well. Nanoparticles show unique physical-chemical properties because of their size. They can be more chemically reactive and can express higher biological activity.

Photography: Neja Stojnić
The connection between nanoparticles and unwanted effects

In the last few years the exposure to nanoparticles has risen because of development of different techonologies. Scientists have figured out, that this leads to a lot of unwanted effects on your health system. Connection was made between nanoparticles in the environment and unwanted effects of respiratory tract and cardiovascular system.

Special physical-chemical properties of nanomaterials lead to forming reactive oxygen species in cells. Reactive oxygen species (ROS) cause oxidative stress. Cells react to this kind of stress with inflammation. Research on rodents had shown that empty nanoparticles have a much higher inflammation effect on the unit of mass than bigger particles with the same chemism.

Inhalation of nanoparticles leads to loading in the lungs, they can also enter the bloodstream and brains. That’s why their use is forbidden in aerosols.

Now before you panic, close your computer and throw all of your sunscreens with nanoparticles away

Nanoparticles don’t work like that when applied to the skin. Our epidermis provides effective protection from effects of the environment. They can pass through the cells, hair follicles or sweat glands. But they don’t pass healthy skin. Damaged skin is another story, in this case the particles can pass the skin, but under what conditions remains unknown.

Why are mineral UV filters in sunscreens in nano size?

Mineral filters in their normal size (200-400nm for zinc oxide and 150-300nm for titanium dioxide) disperse really badly and because of that the application is difficult. They reflect and scatter the light and that causes an unwanted white layer on the skin surface. With the help of nanotechnology we are able to reduce the size of the parcticles under 100nm. With doing that we achieve easier application and transparency.

Photography: Neja Stojnić

Do nanoparticles cross the skin – main subject of scientists

There are a lot of arguments between scientists whether nano sized particles pass the skin barrier and what are the effects of penetrating into the deeper layers. Some studies prove them passing the skin and their toxic effects on the cells, while others disprove this theory.

There are many differences depending on the sort of the vehicle in which we include nanoparticles. Researches had shown that nanoparticles in mineral oil did not pass the skin, while the ones included in O/W emulsion (oil in water – usual for all the creams) did penetrate. Penetration was much higher in the area with a lot of hairs, which shows the penetration through the pores and hair glands.

The smaller the particles, the bigger the chance that they will penetrate the skin. There is a big difference between a particle that is 2nm big and particle that is 50nm big. As we mentioned before, the smaller the particles, the bigger the chance that their properties will change.

Does a regulative on cosmetic field protect us?

We’ll be honest, not really. Cosmetic producers are not obligated to tell what size of  nanoparticles are included in their products. They are obligated to write ‘’NANO’’ next to the filter that is in nano size, but whether this means particles 2nm or 100nm large no one knows, except them.

They represent a big progress in cosmetic industry

Usage of nanometer delivery vehicles is the future. Until now all the cosmetic products contained highly effective ingredients, that manufacturers bragged about. But whether this ingredient will achieve the wanted target in the skin was another thing. Only molecules smaller than 500Da can penetrate in the skin. And if we include a peptide with a molecular mass of 4000Da in our products, it will most certainly not penetrate in the skin. Nano delivery vehicles enable reducing these big molecules into smaller ones, so they can be included to the systems that will reach the target area. This delivery systems are liposomes, dendrimers, solid lipid nanoparticles,..

What is your opinion on nanoparticles in cosmetics?

We’ve already gone through basics about UV rays, protection against UV rays and everyday use of sunscreen. Now it’s time to take a look in the world of compounds that protect us from UV rays – UV filters.

There are two types of UV filters

Organic or chemical and inorganic or physical UV filters. Physical filters scatter and reflect UV rays, while chemical filters absorb them. Physical filters leave a white residue (unless they are nano size), while chemical filters spread quite smoothly.

Sunscreens are usually a mixture of different chemical and physical filters, because with combining them we achieve a broad spectrum protection.

There are even more UV filters then we mentioned in a previous post, so we asked members of a Slovenian Facebook group Ljubim kozmetike to mark the most common filters in their sunscreens. We are going to describe 4 most common ones.

Organic UV filters

Data from studies shows, that organic filters are present in most sunscreens on the market. The most common organic filter is Ethylhexyl methoxycinnamate, since it is present in 80% of all sunscreens. Chemical filters easily absorb in the skin and reach blood circulation. Consequently they can load in different tissues, liver and brain.

Ethylhexyl methoxycinnamate

Oktyl metoxycinnamate (OMC) is a UVB filter known as 2-ethylhexyl-4-metoxycinnamate. As a compound it is allowed for usage in cosmetic products in United States and Europe in concentrations between 7.5-10%. Lots of studies suggest that OMC in an endocrine disruptor, because it can affect excretion of hormones.

After applying of cream with 10% concentration of OMC on the whole body (40g), the filter was absorbed in the skin and was later found in urine and blood. But if we take the highest measured concentration, the complete concentration in 4.7L of blood was only 0.002%.

The positive side of this filter is that it does not irritate the skin and does not cause sensibilisation.

Ethylhexyl salicylate or oktyl salicylate

It’s a organic UVB filter, that absorbs the UV rays. It is allowed for usage in cosmetic products in concentrations up to 5%. This is a filter with relatively good safety profile. Ethylhexyl salicylate possesses an ability to stabilize other photolabile (sensitive to light) UV filters and make them longer lasting. Quite a guy, ha?

This filter has a really low toxic profile. It does not cause irritation or sensibilization, it is not phototoxic and does not cause foto-allergies.

Inorganic UV filters

Inorganic filters used in sunscreens usually contain metal oxide particles, for example titanium dioxide and zinc oxide. These two can be used in concentrations up do 25%, but are usually contained in lower concentration – between 5-10%.

Chemical filters are still dominant in sun-protection products, but the number of products containing only physical filters is rising. One of the reasons why is the fact that they offer a broad spectrum protection – TiO₂ is more successful protection from UVB range, while ZnO is more successful at protection from UVA and UVB1 rays (the protection for UVB range is lower). Using these both filters together provides a broad spectrum protection. Another positive side of using physical filters is absence of irritation and limited skin penetration.

Zinc oxide

Dermal absorption is the main route of entrance for ZnO nanoparticles in our system. Most studies showed that ZnO particles don’t penetrate in deeper layers of the skin. Penetration is significantly higher when the skin barrier is damaged.

Titanium dioxide

Titanium dioxide is commonly used as a white pigment in colors, plastic and paper and as an additive in food. Nanoparticles of TiO₂ are used because of the capability to absorb the UV light in sunscreen products. TiO₂ particles have very low toxicity.

Nanoparticles of TiO₂ can be used in sunscreen products in concentrations up to 25%. Studies show that particles of this filter don’t penetrate healthy or damaged skin. In human keratinocytes it exhibited almost no cytotoxicity, which suggest a very small toxic potential on the skin level.

Exposure to UV filters

We are most exposed to UV filters in a dermal way. Suggested application of sunscreen is 2mg/cm² skin, so that we would reach the protection factor listed on the product. This means we would have to use the whole 40g cream to protect the whole body. At this amount of product, the maximum penetration would be 5% for some organic UV filters. Studies show that amount of product applied is much lower than suggested (less than half). So if we apply a product with SPF 50, the real protection will be probably 25 or less.

UV filters offer a protection from erythema, actinic keratosis and carcinoma. There is also data that sunscreens block normal synthesis of vitamin D and that they act as endocrine disruptors. But in normal usage this is not the case.

What can we conclude?

Usage of UV filters is questionable from aspect of safety. More and more studies show the link between bigger usage of sunscreen products and phenomenon of hormonal and growth disorders. At this point you need to realize that in studies they work with much higher concentrations than allowed. With cosmetic products it is impossible to come in touch with such high concentrations. But we can’t just ignore what the studies say, because side effects can occur within sensitive population. Effects of being exposed to low doses of UV filters for a long period of time are pretty much unknown. Scientists should investigate further and try to find safer compounds to protect us from UV rays.


Sunscreen is essential for preventing skin diseases and premature aging. In conclusion: sunscreen should be used in every season. However, experts started to warn about the importance of protection against UV, but that happened only a few years ago.

There are several types of electromagnetic radiation and one of them is UV radiation. Ultraviolet radiation consists of 3 wavelengths: UVA rays (emitting a wavelength from 320 to 400nm and aren’t absorbed by the ozone), UVB rays (the wavelength from 290 to 320nm, partially absorbed by ozone) and UVC rays (are stopped by ozone) -> well, what’s still left from ozone.

UV radiation has some beneficial effects, such as vitamin D synthesis. It also has a positive effects on the treatment of dermatological problems (acne, psoriasis), bone and joint disorders and childhood diseases. However, there are more negative effects (role in pathogenesis of skin cancer, photo-aging and photo-immunosuppression) than positive.

 UVAUVB
Acute effectsImmediate pigmentation, photosensibilisationErythema, edema, pigment darkening, thicker epidermis, synthesis of vitamin D
Chronic effectsPhoto-aging, immunotoxicityPhotocarcinogenesis, immunotoxicity

UVA rays

UVA rays represent the largest part of solar radiation. They stimulate the formation of reactive oxygen species or ROS. We’ve already been writing about it in blogs (Vitamin C and After 25th, we begin to grow old). UVA rays increase the number of inflammatory cells and reduce the activity of Langerhans cells, which are the first line of defense of our immune system.

UVB rays

UVB radiation causes sunburn. It represents about 18% of total solar radiation and it’s 50-100x stronger than UVA radiation. Our DNA molecules absorb UVB light very well, which can lead to mutation and carcinogenesis. They can damage biomolecules (proteins, lipids and DNA molecules).

UV rays don’t rest!

A few days ago, we’ve asked on Instagram story some questions about your habits regarding to sunscreens and their usage.

57% use the sunscreen only on the beach

56% prefer using sunscreen with a very high protection factor (50, 50+)

69% apply sunscreen several times a day

22% avoids nanoparticles in sunscreens

It’s a bit worrying that more than half of you use sunscreen only at the beach. It’s true that in winter the sun is significantly weaker comparing to summer, but this doesn’t necessarily mean there are no UV rays. In winter while it’s snowing it’s even more likely to get sunburned, because UV rays reflects from snow (white colour reflects sun rays). Despite the fact that there are clouds, who says UV rays can’t pass these clouds to get to us? Again, not so much, but they pass through. Have you ever heard of a friend who went hiking ant the weather was cloudy and came home as red as a beet? Because we have! So this means that UV rays exists even on a cloudy day.

Why is re-application necessary?

Probably, the ones who had answered that apply sunscreen only once, are asking themselves what the hell? You have applied the cream, okay. So you don’t sweat or touch your face? Consequently, by touching and sweating you remove the cream. Also, UV filters stop working after a certain amount of time, meaning they no longer have the effect of protection.

Sun protection products

The main purpose of sunscreens is to protect the skin against the harmful effects of UV radiation. But in order to achieve this effect, it takes more than just choosing the right UV filter in the appropriate concentration. One of the important things is also technological formulation and other ingredients which can support the effect of UV filter or can decompose it.

There is currently a flood of sunscreen products on the market. The SPFs are from 1-50 +. There are products with low protection (SPF 6-10), medium protection (SPF 15, 20, 25), high protection (SPF 30, 50) and very high protection (50+). According to European standards, UVA protection must represent at least 1/3 of the declared SPF.

Recently, we have seen the SPF mark on almost all face products, whether it’s decorative or nourishing. It is especially popular that UV filters are added to the powders, BB and CC creams.

What’s the problem of foundation with SPF15?

If you didn’t just come from the Stone Age, you probably know that for a SPF written on packaging, the application must be 2mg / cm². You probably don’t know how much of sunscreen that is. For a face it is supposed to be used 2 full fingers of cream. We are not 100% sure, but somewhere we’ve found that 70kg man has to use almost the whole sunscreen in order to achieve the SPF protection written on the packaging. Is this even possible? Not really.

Because of the incorrect or insufficient amount (usually 0.8 mg/cm²) of the sunscreen, the actual SPF on our skin is only 20 to 50% of SPF declared on the packaging. So, when using foundation with SPF15, we usually apply a pump or two. This means the actual SPF on the skin is probably barely 3, if not less.

SPF 30 vs. SPF 50

I think that most of us, who have been more or less introduced to the protection against UV rays, know this graph.

This graph shows us that with the protection factor 30, we achieve approximately 95% of protection against UVB rays. With a protection factor of 50, approximately 96.5% of protection. Experts are arguing whether this 1.5% makes a big difference. We must be aware of the amount of UV filters that must be incorporated into the product with SPF 50 comparing to SPF 30. This increased quantity may be unfavorable for people with photosensitivity disorders. If you don’t have them, it’s up to you, if you want to use higher or lower SPF. Keep in mind that you are likely to apply less product and the actual protection is lower.

Types of UV filters

Currently, two types of UV filters are in use, physical and chemical, both of them minimize the previously listed effects of exposure to UV radiation.

Physical or inorganic filters disperse and reflect UV rays while chemical or organic filters absorb them. More and more studies assess the role of these compounds in developmental and endocrine abnormalities, which have been demonstrated in animal and human studies.

Organic UV-absorbing filters are divided into: PABA derivates (PABA, ethylhexyldimethyl PABA), cinnamic acid derivates (ethylhexylmethoxycinnamate, octylmethoxycinnamate), salicylic acid derivates (homosalate), octocrylene, triazine derivates (ethylhexyl triazone), benzophenone derivates (oxybenzone BP-3), sulisobenzone) and dibenzoylmethane derivates.

Among the physical UV filters that reflect and disperse UV rays are zinc oxide and titanium dioxide. Sunscreens are mostly a mixture of several organic and physical UV filters, because with the combination we achieve broad spectrum protection.