UVB Filters and the Endocrine System: Effects of Sunscreens

UVB filters, which are widely used to protect against the harmful effects of sunlight, are one of the main ingredients of sunscreens. However, in recent years, scientific research has increased on the potential effects of these chemicals on the endocrine system. The effects of UVB filters on hormonal balance, thyroid function and reproductive health are being investigated. In this article, we will discuss scientific information about the effects of UVB filters on the body, their relationship with the endocrine system and safe alternatives.

What Are UVB Filters?

UVB filters are chemical or physical compounds that protect the skin by absorbing or reflecting the sun's harmful ultraviolet B (UVB) rays. Chemical UVB filters are usually composed of compounds such as oxybenzone, octinoxate, and homosalate, while physical filters contain mineral-based ingredients such as titanium dioxide and zinc oxide.

Chemical Structures and Areas of Use

Chemical UVB filters are organic compounds that absorb sunlight and convert it into heat after being applied to the skin. These filters are found in many cosmetic products, such as sunscreens, makeup, and moisturizers. Physical filters protect by physically reflecting sunlight and are often recommended for sensitive skin or children.

Effects of UVB Filters on the Body

These filters, also known as physical filters, are particles that scatter and reflect UV rays back through the skin into the environment. They act as a physical barrier to trap ultraviolet and UV light. The most commonly used particulate mineral filters are titanium dioxide and zinc oxide. They are considered broad spectrum because they cover the entire ultraviolet spectrum. Inorganic sunscreens are also called sunscreens, a term derived from their light protection mechanism. The ONLY UV filters approved by the FDA are Zinc Oxide and Titanium di Oxide.

Green algae slow down photosynthesis and growth), causing a decrease in biomass.
Dolphins accumulate in tissues such as the liver and can pass to children through the placenta and breast milk.
Coral accumulates in reef tissues and causes coral bleaching, damages DNA and deforms children; destroys zooxanthellae, leading to death.
Mussels accumulate in lipids and other tissues, causing defects in children.
Sea Urchins damage the reproductive and immune systems. They cause deformation in children.
Fish reduce fertility and reproduction, impair brain and liver functions, stimulate vitellogenin protein production, exhibit estrogenic activity, alter gene transcripts, cause cardiorespiratory stress, lead to neurotoxicity, cause immune system disorders and oxidative stress.
Humans, estrogenic activity, antiandrogenic activity, uterotrophic activity, potential developmental and reproductive toxicity, induction of apoptosis, inflammatory response.

Dermal Absorption Mechanism

Chemical UVB filters can be absorbed by the skin and enter the bloodstream. Research shows that some UVB filters can bioaccumulate in the body and that their levels in the blood increase with long-term sunscreen use.

Chemical (Organic) Filters: Reduces the harmful effects of UV energy by converting it into heat energy and absorbing it, reducing the depth at which it can penetrate the skin. Organic sunscreens work primarily through this mechanism by mixing into the blood.
Mineral (Inorganic) Filters: Scattering and reflection of UV energy from the skin surface. Mineral based (Inorganic sunscreens mainly work with this mechanism.) They provide a coating that prevents the sun's rays from passing through the skin.
Relationship between SPF value and protection: People often assume that applying SPF 50 sunscreen provides almost twice the protection as applying SPF 15. This is not true, because the extra protection provided by a higher SPF value is negligible after SPF 15. SPF 50 sunscreen blocks 98 percent of UVB rays, while SPF 30 sunscreen blocks 97 percent of sunburn rays - the difference is one percentage point.

The internationally accepted thickness of SPF application to the SKIN is 2 mg/cm2 (USA) or 1.5 g/cm2 (EU).

Importance of Bioaccumulation

Bioaccumulation refers to the accumulation of chemicals in the body over time. The detection of substances such as oxybenzone in breast milk and urine in particular raises concerns about the potential health effects of long-term exposure. It shows the main human systems and marine organisms that suffer from the adverse effects of UV filter toxicity. Regarding organic UV filters, some reports have proven their presence in biological samples such as urine and blood samples, especially benzophenone and cinnamate derivatives.

Additionally, many organic UV filters have been reported in collected marine samples, namely: homosalate (algae and brine shrimp); benzophenone-1 (algae) and benzophenone-3 (corals and algae); avobenzone (algae, crustaceans and brine shrimp); EHMC (fish and mussels); octocrylene (brine shrimp, crustaceans and mussels); PABA (mussels) and camphor derivatives (fish). Growth inhibition was one of the adverse effects affecting algal organisms, namely Tetraselmis sp.

ZnO nanoparticles are widely used in sunscreens and UV protectors. Unlike larger particles, nanoparticles can easily pass through the skin and biological membranes, thus penetrating various cells, tissues and organs. When mixed with the blood, they can circulate throughout the body and reach vital organs and tissues. According to the hypothesis, high amounts of nanoparticles entering the body trigger stress reactions by creating an overload in the phagocyte cells of the immune system. This can lead to inflammation and weaken the body's defense mechanisms. In addition, the chemical reactivity of nanoparticles can increase the formation of free radicals, causing damage to proteins, cell membranes and DNA. DNA damage can lead to mutations and trigger cancer development. However, the toxicity of nanomaterials and their long-term effects on the organism have not yet been fully determined and the current information is at a hypothetical level. In order to understand the possible effects of nanomaterials on the ecosystem, extensive research needs to be conducted on wastewater, drinking and utility water, surface water, soil, air and plants.

Relationship Between the Endocrine System and UVB Filters

Some UVB filters are classified as endocrine disrupting chemicals (EDCs). Endocrine disruptors can alter the body's natural hormone balance by interfering with the hormonal system. Benzophenone-3 (oxybenzone) is a broad-spectrum UV filter that absorbs UVB (290-320 nm) and UVA (320-340 nm) rays. It is widely used in sunscreens, hair sprays, and colored cosmetics. There are many studies that it can cause allergic reactions, endocrine disrupting effects, and environmental damage. Initially, it was permitted to be used up to 10% in sunscreens in Turkey and the EU, but this limit was reduced to 6% in 2017. The FDA also determined this rate as 6%, and its use was banned in Hawaii. In a study conducted in the US between 2003-2012, benzophenone-3 was detected in the urine of 96.8% of volunteers.

Higher concentrations were found in women and high-income individuals. While 0.4% of benzophenone-3 was detected in urine 48 hours after the application of sunscreens, another study showed that the dermal absorption rate was 2%. Benzophenone-3 is rapidly absorbed from the skin and reaches maximum plasma levels within 4 hours. Since its molecular weight is 228.26 Da, it can easily cross the skin barrier. Similarly, benzophenone-8 is rapidly absorbed from the skin. However, it has been found that by synthesizing dioxybenzone in polymer form, skin penetration decreases and the same level of UV protection is provided.

The Organisation for Economic Co-operation and Development (OECD) has published a document containing standardised tests to assess potential endocrine disrupting chemicals. Accordingly, potential endocrine disruption by UV filters has already been reported in biological samples, namely placenta and human sperm. Witorsch et al. (2010) mentioned the adverse effect of some classes of compounds, including UV filters that penetrate skin layers; however, this study highlighted that serum and reproductive hormone levels were not affected by this exposure.

Recently in 2016, Rehfeld et al. studied the in vitro effect of UV filters on male fertility, assuming the possibility that UV filters mimic progesterone, considering that both the hormone and the UV filter can interfere with Ca2+ channel signaling and consequently activate certain biological processes. Various research groups have reported other adverse effects of UV filters using in vivo models such as rats, insects, fish, among others. Estrogenic, androgenic, and thyroid activities are included in the endocrine disrupting effects of UV filters.

Effects on Hormone Balance

UVB filters such as oxybenzone and octinoxate have been shown to interact with the hormones estrogen and androgen. This can disrupt hormonal balance and pose potential health risks. Various organic UV filters are absorbed systemically and therefore may affect endocrine processes, therefore they are classified as endocrine active chemicals (EACs) [ 49 ]. Some of the more relevant UV filters are benzophenones or those derived from cinnamates or camphor.

Changes in Thyroid Functions

Some studies suggest that UVB filters may have thyroid hormone-disrupting effects. Specifically, they may interfere with the mechanisms that regulate the production and metabolism of thyroid hormones, increasing the risk of hypothyroidism or hyperthyroidism.

Animal Studies:

UV filters such as BP-3, OMC and 4-MBC have been found to have effects on thyroid hormones in various animal models.
BP-3 and OMC demonstrated thyroid receptor-mediated transcriptional activation in vitro.
4-MBC increased TSH and decreased thyroxine (T4) levels by reducing iodine uptake in rats.
OMC decreased T3 levels and TSH receptor expression.
4-MBC was observed to increase thyroid weight in both parent and offspring mice.
Although some studies have shown changes in thyroid hormone levels in animals exposed to UV filters, the functional effects of these changes are not always clear.

Human Studies:

The study by Janjua et al suggested that UV filters do not disrupt the homeostasis of human thyroid hormones.
Other studies (case-control, cohort, and cross-sectional) have not found a significant or consistent association between BP-3 and thyroid hormone levels.

Overall Result:

UV filters can be taken into the body through environmental exposure or topical use.
It has been shown to affect hormonal pathways in animal studies, but human data are inconclusive.
The effects of UV filters on the human endocrine system are still unclear and further research is needed.

Effects on Reproductive Health

It is thought that some UVB filters may have negative effects on reproductive health due to their endocrine disrupting effects. It is suggested that they may reduce sperm quality, especially in men, and affect fertility by causing hormonal imbalances in women.

Effects on Pregnancy and Development:

Santamaria et al. (2020): BP-3 taken via dermal absorption during pregnancy caused intrauterine growth retardation, change in sex ratio and deterioration in the growth chart of the offspring.
Downs et al. (2015): BP-3 exposure decreased body weight, increased prostate weight by 30%, and led to a significant increase in uterine weight in childhood in mice.

Overall Result:

BP-3 can disrupt hormone balance by exhibiting estrogenic and anti-androgenic effects.
Mouse and fish studies suggest that BP-3 may have adverse effects on the reproductive system and development.
Long-term effects on humans are unclear, but should be evaluated carefully due to its endocrine disrupting potential.

Groups at Risk

Pregnant Women and Developing Fetuses:

UVB filters (e.g. benzophenone-3, octinoxate, 4-MBC) can cross the placenta and reach the fetus.
Intrauterine growth retardation, changes in sex ratio, and hormonal imbalances have been observed.

Babies and Children:

Because their hormonal systems are still developing, they may be more affected by estrogenic and anti-androgenic effects.
There are risks of early puberty, developmental disorders and weakened immune systems.

Women and Men of Reproductive Age:

It can disrupt the balance of estrogen and androgen, which can lead to negative effects on fertility.
It can lower testosterone levels in men and cause an increase in prostate weight.
In women, menstrual irregularities and effects on the reproductive system may occur.

People with Hormonal Imbalance or Endocrine Disease:

Those with thyroid diseases, polycystic ovary syndrome (PCOS), diabetes and other endocrine diseases may be more sensitive to the hormonal effects of UVB filters.

Individuals Who Use Heavy Sunscreen (Especially Daily Users and Athletes):

Frequent use of sunscreens and skin care products containing UVB filters can cause high levels of absorption through the skin.
Those who spend long periods of time in the sea or pool may be exposed to the environmental effects of UV filters and thus pose an additional risk.

Things to Consider During Pregnancy

The content of the sunscreen is of great importance when using sunscreen during pregnancy. It has been shown that endocrine disrupting chemicals such as oxybenzone can cross the placental barrier and have an effect on the fetus. Therefore, it is recommended that pregnant women prefer mineral-based sunscreens.

Use in Children

Children should be careful about sunscreen use because their skin barrier is more permeable than adults, and they may be more exposed to chemical UVB filters. Therefore, it is a safer option to choose mineral-based sunscreens for children.

Safe Alternatives

Safe alternatives can be preferred to chemical UVB filters, which are thought to have negative effects on the endocrine system. Mineral-based filters: zinc oxide, titanium dioxide should be preferred as safer sunscreens.

Mineral Based Preservatives

Sunscreens containing zinc oxide and titanium dioxide reflect sunlight by creating a protective barrier on the skin's surface. It is known that these minerals are not absorbed by the skin and do not affect the endocrine system.

Natural UV Filters

Some plant oils, multicosmetic solutions , and extracts may have natural sunscreen properties. For example, carrot seed oil and raspberry seed oil may naturally provide low SPF values. However, since they do not offer as strong protection as traditional sunscreens, extra precautions should be taken.

Conscious Use Suggestions

Avoid prolonged and excessive use of sunscreens containing chemical filters.
Choose mineral-based sunscreens for children and pregnant women.
When using daily sunscreen, check for ingredients that may have a negative effect on the endocrine system.
Look for safe, natural sunscreens that do not contain UVB filters.
Instead of relying solely on sunscreen to protect yourself from the sun, use physical protection methods such as hats and long-sleeved clothing.

Conclusion Although UVB filters play an important role in protecting against harmful sun rays, the possible effects of some chemical filters on the endocrine system should be considered. Safer sunscreens should be preferred, especially for children and pregnant women. Mineral-based sunscreens and natural filters are more reliable options in terms of protecting skin health and not affecting hormonal balance.

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