Research Question

Neutrogena is a common brand of sunscreen used by consumers. We wanted to identify the primary ingredients in the sunscreen to analyze any potential toxic effects after exposure to UV radiation. Do sunscreen ingredients increase the risk for cancer? Also, if toxic, do the dangers outweigh the protective benefits of sunscreen against UV radiation?

Introduction


It may be considered attractive to be tan, but a tan is really the human body’s mechanism of protecting itself. Males and females expose themselves to Ultraviolet, UV, radiation to acquire pigmentation in their melanocyte cells. This pigmentation is called melanin, and it is cells’ defense mechanism against damage by UV radiation. The melanin produced by UV exposure darkens skin color to produce what people perceive as a tan.[8]

The Skin Care Foundation states, “Nearly 30 million people tan indoors in the U.S. every year; 2.3 million of them are teens.” [7] The tanning culture has influenced people to increase their sun exposure, downplaying the risks of skin cancer. Individuals still tan without sunscreen even when they are educated on the risks of sun exposure. It is estimated by the American Cancer Society that over “2 million basal and squamous cell cancers are diagnosed each year.” [9] Basal cell skin cancer is more common than squamous cell. While basal and squamous cell skin cancer is not typically found in young adults, the sun exposure habits when one is young affect the risk of developing cancer in one’s fifties.

An important factor in sun exposure habits is one’s use of protective sunscreen. Sunscreen, when applied correctly and with the correct dosage, is designed to absorb UV radiation. Sunscreen is sold at various SPF levels and typically protects against UVB wavelengths. Recently, UVA wavelengths have been associated with skin damage and skin cancer, so products now include broad-spectrum ingredients to also include UVA protection. There are tests that determine the SPF of a sunscreen product, however studies have shown speculation that these tests are not reliable measures of protection against UVB radiation. In addition, there is no test to measure how effective broad-spectrum ingredients are in absorbing UVA radiation. As mothers tell their children, “Do not forget to put on sunscreen, you do not want cancer,” the question at hand is if sunscreen is as effective as it is labeled based on current testing strategies.

UV Radiation


uvradiation3.jpg
The wavelength of UVAradiation is between 320-400nm and it is present in 95% of the UV radiation that penetrates Earth's atmosphere. The wavelength affects keratinocytes in the basal layer of the epidermis and is responsible for pigmentation. The wavelength of UVB radiation is between 290-320nm. This wavelength reaches only the superficial layers of the epidermis. UVB is the primary cause of erythema, redness of the skin, also known as
sunburn.[7]

Types of Skin Cancer

Nonmelanoma Skin Cancer


Basal Cell Carcinoma
Basal Cell Carcinoma (BCC) is the most common human cancer that occurs predominantly on sun-exposed skin in elderly fair-skinned patients. According to American Cancer Society, more than 1,000,000 new U.S. cases will be diagnosed this year, but fortunately they are highly curable.[9]

Basal_Cell_2.jpg
Skin cancer - basal cell carcinoma
Skin cancer - basal cell carcinoma


Squamous Cell Carcinoma

Squamous Cell Carcinoma (SCC), which is the second-most type of skin cancer, and spreads faster than Basal Cell Carcinoma (BCC) usually occurs on areas exposed to the sun. Sunlight exposure and immunosuppression are risk factors that result injury and inflammation of skin. SCC in its earliest form appears as large (often larger than 1 inch), reddish patches, or a growing bump that may have a rough, crusty surface and flat reddish patches. Bumps are usually located on areas such as face, neck, ears, arms, or hands. Some of the risk factors for SCC include: [7]
  • Having light-colored skin, blue or green eyes, or blond or red hair
  • Long-term, daily sun exposure (such as in people who work outside)Many severe types of sunburn early in life
  • Older age
  • A large number of x-rays
  • Arsenic
  • chemical exposure

Doctors tend to get skin biopsy, and carefully check the skin and examine the size, shape, color, and texture of any suspicious area. As far as treatment, like many other types of cancer, SCC has a high chance of cure if it is diagnosed in its early stages. But treatment generally depends on how big the tumor is, its place and position, and how far it has spread. Some of these practical treatments are:[7]
  • Cutting out the tumor
  • Mohs surgery
  • Radition
  • Skin creams
  • Photodynamic therapy

One of the most important ways in preventing SCC is reducing sun exposure, and protecting the skin by wearing hats, long sleeved shirts, and pants. Also, using high-quality sunscreens(water proof formula) with SPF rating of at least 30 that effectively prevents against UVA and UVB sunlight, and using that in proper manner (applying sunscreen at least 30 minutes before going outside and reapply it frequently) can be a helpful way to prevent Squamous Cell Carcinoma.

Melanoma

According to Anastasia Petro,M.D, and Jennifer Schwartz, M.D, "Melanoma is a malignant tumor that is made up of abnormal melanocytes. Normal melanocytes, which reside in everybody's skin, are cells that produce a brown pigment called melanin. Melanin is the major determinant of a person's skin color and also serves as the body's own natural sunscreen."[11] A melanoma develops when certain melanocytes are no longer able to control their own growth and continue to multiply at a fast rate. This phenomenon occurs when melanocytes undergo significant damage. Too much exposure to sunlight, especially enough to cause blistering or peeling sunburns during childhood, can result in enough cellular injury to cause melanoma as well as other skin cancers. In addition, there are other factors that make a person more susceptible to developing a melanoma.[11] These include:
  • Blond or red hair, blue eyes, or fair skin ·
  • More than 100 normal moles or many unusual moles
  • Previous history of a melanoma
  • Blood relative(s) with a melanoma

UV Damage


DNA


" One important DNA damage response is triggered by exposure to UV light. Of the three categories of solar UV radiation, two types of UV radiation (UVA & UVB) are of greatest concern to humans, especially as continuing depletion of the ozone layer causes higher levels of this radiation to reach the planet's surface. Relatively flexible areas of the DNA double helix are most susceptible to damage. In fact, one "hot spot" for UV-induced damage is found within a commonly mutated oncogene, the p53 gene " says Suzanne Clancy, Ph.D.[10]

Studies show that every third white person born after 1994 developed at least one BCC. BCC patients are less efficient at repairing UV-induced DNA damage. UVB causes DNA damage, and chromosome break through point mutation: {C-->T (Transition), CC-->TT dimer formation (Mutation)}.[12]
Untitled.jpg
Pathogenesis of BBC occurs mostly with implications in several tumor suppressor genes and proto-oncogenes. Mutation pathways are complicated. One of the most famous pathways is TP53 tumor suppressor gene (a member of the RAS proto-oncogene family).
"The following sequence is thought to be responsible for skin carcinomas: UV radiation (UVR) reaches the epidermal cell layer where the precursor cells of these tumors are located; UVR is absorbed by DNA and induces DNA alterations in some genes within these cells. The most significant mutations occur in tumour suppressor genes. The p53 gene for SCC and BCC, and the patched gene (PTCH) for BCC are major targets of UVR. The inactivation of these genes leads to cell proliferation. UVR-induced DNA alterations occur mainly at neighboring pyrimidines, causing dimers (C-T, CC-TT base substitutions at dipyrimidine sites). They are considered a UV signature.”[13]

Immunosupression


UVA radiation is primarily responsible for suppression of immune responses, however UVB is also believed to have a role. Immune system suppression can be found at levels of UV radiation even before sunburn occurs. While the level of immunosuppression by UV radiation varies from individual to individual, those who are more susceptible to immunosuppression are also more at risk for melanoma and nonmelanoma skin cancers.

Sunburn


Sun exposure can cause first and second degree burns:[16]
  • First-degree burns affect only the outer layer of the skin. They cause pain, redness, and swelling.
  • Second-degree (partial thickness) burns affect both the outer and underlying layer of skin. They cause pain, redness, swelling.
First degree burn
First degree burn
Second degree burn
Second degree burn

Sunscreen Protection


Physical vs. Chemical Protection

There are two methods by which sunscreen can protect skin. Sunscreens contain different ingredients that act as either physical UV radiation filters or chemical UV radiation filters. Physical filters such as Zinc Oxide and Titanium Oxide block UV radiation from penetrating the skin (They act by scattering, reflecting, or obsorbing UVradiation). The inorganic compounds diffract UV light. These ingredients protect against UVA and UVB radiation and are better for sensitive skin. Chemical filters absorb UV radiation by converting the energy in the light so that it cannot damage skin. These organic filters work within the skin. There are many chemical filters, but each absorbs only a certain wavelength. Therefore, these organic chemical filters have to be combined in sunscreen to provide full spectrum protection.[14]

Chemical Absorption

Absorption_Table.png


Commonly used chemical sunscreen ingredients have been found to have good ab
sorption across the stratum corneum according to a study conducted by H.A.E. Benson.[15] Absorption was measured based on topical application and the detection of chemicals in urinary excretion breast milk following application. Results from tape-stripping methods also supported the presence of active ingredients such as Benzophenone (Oxybenzone), Butyl methoxydibenzoylmethane, and Octocrylene.[15]
The examples of commonly used chemical sunscreen active ingredients and their UV absorption rate is shown in this table.

Toxicity of Sunscreen

"Acute toxic adverse effect of specific sunscreen agents include contact irritation, allergic contact dermatitis, phototoxicity, photoallergy and staining of the skin."[15]. "Relatively little information is available on the mutagenic and carcinogenic potential of sunscreen agents.

It has been suggested that certain sunscreen agents may have mutagenic effects if absorbed into the skin. As stated in a study by H.A.E Benson, "The mechanism of mutagenicity is suggested to be due to the generation of free radicals, the same as that implicated in UV induced skin damage and cancer. The authors (J. Nishi, R. Ogura, M. Sugiyama, et al.) suggested that any UV light which passes through a sunscreen and reaches dividing cells is likely to be particularly damaging if octyl dimethyl-p-aminobenzoate (padimate 0) has entered those cells. Other common sunscreen agents with similar chemical structures, for example, butyl methoxydibenzoylmethane (Avobenzone), padimate A (amyl dimethyl-paminobenzoate) [withdrawn in 1989] and benzophenone-3, may have similar effects on dividing cells under UV illumination."[15]

Neutrogena Sunscreen As an Example


Neutrogena, one of the leading manufactures of sunscreen products, has patented its Helioplex sunscreen technology. Neutrogena sunscreens containing Helioplex use Avobenzone and Oxybenzone as the primary active ingredients. When this research was conducted, it was only known that Avobenzone, Oxybenzone, and an inactive ingredient Diethylhexyl 2,6-naphthalate were present in Neutrogena Helioplex sunscreen.[1]

Neutrogena states “Avobenzone is one of the best UVA blockers approved by the FDA, but it is highly unstable when exposed to sunlight.”[1] In a study conducted on the stability of Avobenzone , it was concluded that Avobenzone is stable throughout irradiation only if it is in a polar protic solvent. Otherwise, Avobenzone can spontaneously photoisomerize from the enol to the keto form upon energy from radiation.[2]Avobenzone.jpg














This process releases free radicals and the keto form can further undergo photodegradation that also produces free radicals. In addition, the degraded keto-isomer no longer absorbs UVA wavelengths. The keto-isomer can no longer revert back to the enol-isomer, thereby also reducing the level of protection against UVA radiation.[3]


Keto-enol.jpg
Avobenzone_Stabilization.jpg



In the Helioplex technology, two strategies have been included to prevent the affects of photo instability in Avobenzone. First, pairing Avobenzone with complimentary active ingredients can provide photo stability.
Avobenzone is more stable in the presence of the active UVB filter ingredient, Oxybenzone. [4] A study showed that Avobenzone on its own degraded by “about 60% after 1 hour and 90% after 4 hours of UVR exposure.” This figure shows that 10% Octocrylene with Avobenzone was the best photo stabilizer, maintaining Avobenzone’s enol-isomer chemical structure for 4 hours after exposure. 6% Oxybenzone followed closely behind, maintaining 70% of Avobenzone’s chemical structure.[4]






In addition, Neutrogena includes diethylhexyl 2,6-naphthalate, DEHN, which also prevents the affects of photo instability in Avobenzone. The molecule binds to the excited (triplet state) enol-isomer of Avobenzone and prevents the structure from rearranging to the keto-isomer.[3,5] This thereby reduces the amount of free-radicals produced as well as maintains Avobenzone's ability to absorb UVA radiation.

Oxybenzone.jpg
The Oxybenzone (B3) ingredient, that has absorbance in the UVB region, has also been found to have adverse effects.
Upon irradiation, Oxybenzone passes through a higher energy level, which is believed in cellular environments, to achieve a lower energy state by reacting with singlet oxygen. This singlet oxygen can further react and produce superoxide radical anions. [6] These reactive oxygen species (ROS) can react with DNA and cause mutations. A study [6] observed the amount of ROS present naturally in skin as compared to the amount after irradiation and with various UV filters. Oxybenzone reduced the amount of ROS on the skin surface immediately after exposure to UV radiation compared to the crème control. However, after 60 minutes, the mean amount of ROS was more than the control. The study suggests that Oxybenzone increases the amount of ROS present in skin cells.



Oxybenzone_ROS.jpg



In summary, when irradiated Avobenzone undergoes a chemical change resulting in free radicals. The ROS produced by Oxybenzone are also a type of free radical. Free radicals have an unfilled p-orbital that causes the molecule to be more reactive. To achieve a lower energy state, radicals bind to other molecules. The radicals can bind to DNA causing damage that could lead to cancer.

Conclusion


The purpose of sunscreen is to protect skin cells from UV radiation that penetrates through the epidermis and damages DNA. A sunscreen would not serve its purpose if the ingredients involved contribute to more DNA damage. Studies have found that the individual ingredients in Neutrogena Helioplex technology sunscreen have potentially dangerous effects. However, Avobenzone has been stabilized through its coupling with Oxybenzone and DEHN. On the other hand, Oxybenzone is still potentially dangerous because it produces higher ROS levels after 60 minutes of irradiation than the creme control. Yet the study also showed that after 20 minutes of irradiation, Oxybenzone reduced the amount of ROS levels compared to the crème control. Thus, Neutrogena sunscreen can still be safe if it is reapplied every 20 minutes in sufficient amounts.

Also, the significance of the Oxybenzone study is questionable because while Oxybenzone increases the amount of ROS, there is a lack of research available to prove that this increase is significant in causing DNA damage. There are a number of cellular processes that occur naturally that result in oxidative products. A certain level of oxidative products is necessary in the body, however it is unknown as to what concentration of oxidative products is necessary as opposed to damaging. While the ROS figure shows that Oxybenzone produces more ROS compared to the control, this amount may not cause damage.

In addition, the safety of Neutrogena’s formula could be improved by substituting Oxybenzone with Octocrylene. As seen in the above Avobenzone Stability figure, Octocrylene stabilized Avobenzone better than Oxybenzone over the course of four hours. Octocrylene also produced lower ROS levels; the mean value was closer to the mean value of the crème control after 60 minutes. Octocrylene, like Oxybenzone, also absorbs UVB wavelengths. Neutrogena sunscreen would still have broad-spectrum protection with fewer free radical byproducts.

Although some findings show that sunscreen ingredients can be dangerous, reapplication every 20 minutes reduces the toxicity. The potential toxicity is also not significant in damage as compared to the alternative; not using sunscreen and potentially getting cancer.

References


[1] Neutrogena Website
[2] Photostability of the sunscreening agent 4-tert-butyl-4′-methoxydibenzoylmethane (avobenzone) in solvents of different polarity and proticity

[3] Sunscreen Photostability 101.

[4]Characterization of the UVA Protection Provided by Avobenzone, Zinc Oxide, and Titanium Dioxide in Broad-Spectrum Sunscreen Products.

[5] Influence of the Photostabilizer in the Photoprotective Effects of a Formulation Containing UV-Filters and Vitamin A.

[6] Sunscreen enhancement of UV-induced reactive oxygen species in the skin.

[7] Skin Cancer Foundation Website
[8] Function of Skin Pigment
[9] American Cancer Society
[10]DNA Damage Repair Mechanisms for Maintaining DNA Integrity
[11] Melanoma Watch Your Back
[12]The Mechanisms of UV Mutagenesis

[13] Carcingogenesis of Basal Cell Carcinoma
[14] Sunblock
[15]Assessment and Clinical Implications of Absorption of Sunscreen Across the Skin
[16] Burns