FOREWORD

1. INTRODUCTION

The sun emits ultraviolet (UV) rays, specifically UVA and UVB, a portion of the electromagnetic range. UVA wavelengths extend from 400 to 320 nm, while UVB wavelengths extend from 320 to 290 nm (D’Orazio et al., 2013). UVA beams can enter both the upper layer of skin (the epidermis) and the lower layer (the dermis), frequently harming keratinocytes within the epidermis where skin cancer ordinarily starts. Although UVB rays don't enter the dermis, they are more penetrating due to their shorter wavelengths. Both types of UV rays can harm humans, causing sunburns, skin cancer, and other skin damage (Cadet & Douki, 2018); (Sander et al., 2020) ; (Tang et al., 2024). More than 1 million people in the United States are diagnosed with skin cancer each year (Prakash et al., 2015). To mitigate these risks, the use of sunscreen is commended.

Sunscreen secures the skin by absorbing or reflecting harmful UV beams, preventing them from coming to it. Utilizing sunscreen during sun exposure can significantly reduce the risk of skin cell damage and cancer development. Sunscreens are designed to protect the skin from the harmful effects of the sun, including immediate effects like erythema (sunburn) and long-term effects like actinic photo-aging and skin cancers.

The efficacy of sunscreen against UVB in humans is evaluated based on the minimum erythemal dose (MED). This test involves applying sunscreen to a volunteer's skin, exposing protected and unprotected skin to UV rays from a solar simulator, and determining the doses necessary to cause minimal sunburn on each volunteer's protected and unprotected skin (MEDp and MEDu). The individual SPF is the ratio of these two doses (SPF = MEDp/MEDu). The product's SPF is the average of individual SPFs from multiple volunteers. Sunscreens are formulated to contain appropriate amounts of UV-absorbing substances. They are assigned sun protection factors (SPF) to indicate their level of protection against UV radiation (Sabzevari et al., 2021).

These measures are crucial for individuals' well-being, as exposure to UV radiation, particularly UVB, can lead to various health issues, including sunburn, skin cancer, immune system deficiencies, and eye damage (Behar-Cohen et al., 2013). Microfine metal oxides like zinc oxide and titanium dioxide have effectively protected against UV rays by activating electrons within their atomic structure and absorbing UV radiation (Singh & Nanda, 2014; Threes Smijs, 2011). Consequently, zinc oxide and titanium dioxide have become significant subjects of scientific research. Nanotechnology, which involves manipulating particles at the atomic and molecular levels, is already present in various products and is expected to become even more important (Fonseca & Rafaela, 2013).

Historically, SPF evaluation has been performed in vivo on human volunteers (Bendová et al., 2007), following the COLIPA method, is based on the minimal erythemal dose related primarily to the biological effects of UVB irradiation (Honari & Maibach, 2017). The effectiveness of sunscreen formulations and factors influencing sun protection were studied (Portilho et al., 2023). The actual SPF values of products body creams and lotions were calculated using Mansur’s formula (Mbanga et al., 2014); (Andrea et al., 2022; Omar & Abdulrahman, 2015). Evaluation studies of the sunscreen cream like diffusion studies, and estimation of SPF were also carried out (Cedrick et al.), 2024) Some articles comprehensively review existing sunscreen testing standards, discussing challenges and opportunities in improving analytical methods (Zou et al., 2022). A key objective was to examine both in vitro and in vivo SPF values of natural 90% pterostilbene extracted from Pterocarpus marsupium (Majeed et al., 2020). The study further explores the comparison of UVA-PF measurement protocols, highlighting advancements in nanotechnology-based sunscreens, which enhance UV protection through improved safety and efficacy (Chavda et al., 2023).

This research aimed to determine the in vitro SPF values of several commercially available sunscreen markets in Erbil City by UV-Vis spectroscopy and compare the results with the label-claimed SPF values. Additionally, the study examined the UVA and UVB ratio, energy gap, and refractive index of these sunscreens.

2. MATERIAL METHODS

The Materials And Specimens.

Analytical-grade ethanol (98%) was purchased from Fluka. Commercially available sunscreen formulations with SPF values of 15, 50, 60, 80, and 100 from various brands were acquired from pharmacies and other stores that sell these products.

The Instruments

UV measurements were carried out utilizing the Shimadzu UV-Vis mini 1240 spectrophotometer as shown in Figure 1(a). All samples were measured in 1 cm quartz cells.

Methods Of Sample Preparation

1.0 g of all samples were weighed, transferred to a 100 mL volumetric flask, diluted to volume with ethanol, followed by ultrasonication for 5 min, and then filtered through a cotton filter, rejecting the ten first mL. A 5.0 mL aliquot was transferred to a 50 mL volumetric flask and diluted to volume with ethanol. Then a 5.0 mL aliquot was transferred to a 25 mL volumetric flask and the volume was completed with ethanol. The final solutions were sealed in quartz vials.

UV Absorption Measurement And Physical Properties

After preparation, all samples were scanned at wavelengths between 200 and 400 nm. The Mansur equation was applied to calculate the SPF values at the end of all measurements.

After preparing, the sample solution's absorption spectrum was measured in the 200 to 400 nm region using a 1 cm quartz cell and ethanol as a blank. The absorption values were acquired in the range of 290 to 320 and every 5 nm, The samples' SPF was determined using the Mansur equation. (Mishra et al., 2011).

Here, CF = correction factor (10), EE (λ) = arrhythmogenic effect of radiation with wavelength λ, and Abs (λ) =spectrophotometric absorbance values at wavelength λ. The values of EE (λ) x I are constants. They were determined by Sayre et al and are given in Table 1(Das et al., 2017).

Table 1. Values of EE (λ) x I at a different wavelength

Wavelength	Value of EE x I
290	0.0150
295	0.0817
300	0.2874
305	0.3278
310	0.1864
315	0.0837
320	0.0180

The UVA/UVB protection ratio is an essential metric for evaluating a sun protection product's ability to protect against UVA and UVB radiation. Our research testing service can reliably analyze the UVA to UVB protection ratios of various sunscreens and sunblocks. We carefully evaluate those products' UVA and UVB filters for their relative effectiveness. With this information, beauty firms may confidently sell their sun protection products, giving customers reliable evidence of their products' balanced protection against UVA and UVB rays.
Recognizing the UVA to UVB protection ratio allows consumers to make informed decisions when choosing sun protection solutions that meet their needs. This knowledge empowers them to choose products that provide optimal protection against UVA-induced premature aging and UVB-induced sunburn and skin damage. The optimal protection ratio to assure adequate protection in both regions of the UV spectrum is about 1:1 UVA to UVB. To offer optimum protection, you want an SPF factor no more than three times higher than the UVA protection factor.

Even with these benefits, there are potential drawbacks to using products with extremely high SPFs. After SPF 50, which blocks around 98 percent of UVB rays, the increase in UVB protection is minimal. Additionally, while UVA protection is crucial as it contributes to skin aging and may even cause skin cancers, SPFs primarily measure UVB protection. People who use high-SPF sunscreens might not get sunburned, since UVB is the main cause, but they may still be exposed to large amounts of skin-damaging radiation if the sunscreen lacks UVA-screening ingredients. The relative index UVA to UVB is calculated in equation (2):

The refractive index of the samples was measured using a refractometer setup, as shown in Figure 1(b). The refractometer is an optical instrument to acquire a reflection spectrum over a visible wavelength range. It consists of two arms, or telescopes, whose axes lie in one plane. One telescope is stationary, while the other rotates around a central axis that intersects the two telescope axes perpendicularly. The angle between the two telescopes is read on a 360-degree graduated circle. A light source (He-Ne laser with a wavelength of 632.8 nm) provides the light for measurements. The light is depolarized, and a rotating polarizer allows the polarization of light to be selected. Another polarizer called the analyzer, is placed before the detector. The output from the PIN silicon detector is connected to a digital meter. This instrument was used to determine the variation of relative reflectance versus the angle of incidence, which was then used to determine the refractive index of the sunscreens.

Figure 1: (a) Schematic of UV-visible spectroscopy setup and (b) Refractometer experimental setup used to measure the refractive index of samples.

3. CALCULATION AND RESULTS

Calculate SPF And UVA/UVB Ratio Of Sunscreens

SPF 15 (Sample S1)

Figure 2 demonstrates the absorbance spectrum for the S1 sample against wavelength. It clarifies that the high absorbance peaks occurred in the 300 nm and 200 UV regions. The SPF of sunscreens and relative indexes were calculated utilizing equations (1), and (2). This sample has a low SPF of 12 and a ratio of UVA to UVB 0.949, which sets it apart from the other samples

Figure 2: The absorbance spectrum for the S1 sample.

SPF 50 (Samples S2, S3, S4, and S5)

Figure 3 demonstrates the absorbance spectra for the S2, S3, S4, and S5 samples. The calculated SPF factors were 36.86, 43.84, 50.76, and 49.76. The calculated relative index UVA/UVB ratios are 2.715, 2.620, 2.469, and 2.470 respectively. they show that each sample's relative ratio is roughly equal.

Figure 3: The absorbance spectra for S2, S3, S4, and S5 samples.

Spf 60 (Sample S6)

Figure 4 demonstrates the absorbance spectrum of S6. It indicates that the S6 sample has a high ultraviolet absorbance. The calculated SPF factor was 50.25. The calculated relative indexes UVA/UVB ratio was 0.775 indicating that the sample has a lower SPF than the label SPF.

Figure 4: The absorbance spectrum for the S6 sample.

Spf 80 (Sample S7)

Figure 5 demonstrates the absorbance spectrum versus wavelength. Based on this figure, it was determined that sample S2 had a high absorbance in the UVB and UVA regions. The calculated SPF factor was 60 lower than what is stated on the label. The relative index of UVA to UVB ratio is 1.88.

Figure 5: The absorbance spectrum for the S7 sample.

Spf 100 (Sample S8)

Figure 6 demonstrates the absorbance spectrum as a function of wavelength. It clarifies that the S8 sample has a very low absorbance of 0.25 for UVA and UVB regions. The computed SPF of this sample is very low at 80 compared with the label SPF factor is 100. The relative UVA / UVB ratio is 2.48.

Figure 6: The absorbance spectrum for the S8 sample.

4. DISCUSSIONS

The SPF And UVA/UVB Ratio Of Sunscreens

The Spectral absorption of sunscreens S1, S2, S3, S4, S5 S6, S7, and S8 samples are presented in Figures 2, 3, 4, 5, and 6 respectively. The investigation of spectra designated as products for UVA and UVB protection. Since UVA radiation is in the range 320- 400 nm and UVB in the 290-320 nm range it is obvious from the given results that sunscreen S1 gave good results, since they showed absorption peaks, both in UVA and UVB region, nearly equal to 1. Product S1 has one good pronounced peak in the UVA range and is less pronounced in UVB in contrast, The other samples did not show absorption in the UVA and UVB spectrum. Table 2 indicates the computed value and the labels SPF with relative index UVA/UVB ratio for S1, S2, S3, S4, S5, S6, S7, and S8 samples. The results showed that 25% of the analyzed samples closely matched the labeled SPF, 12.5% had SPF values higher than labeled, and 62.5% had SPF values lower than labeled.

The UVA/UVB ratio helps determine if a sunscreen offers broad-spectrum protection, effectively shielding against both types of rays. Broad-spectrum sunscreens reduce the risks of both immediate sunburn (from UVB) and long-term aging or cancer risk (from UVA). The ratio is particularly relevant in ensuring that UVA protection is not neglected in formulations. Sunscreens with a high SPF often primarily target UVB protection (since SPF mainly measures UVB effectiveness). However, without adequate UVA protection, users may be at risk for photoaging and deeper skin damage. By ensuring a balanced UVA/UVB ratio, sunscreens provide comprehensive protection. In a standard defined by dermatology and photobiology experts, a UVA/UVB ratio of around 1/3 is often used as a guideline to balance the potential damage from both types of radiation. This ratio attempts to limit UVA exposure while still allowing some level of UVB for benefits like Vitamin D production. the exceeds our results of UVA/UVB ratio from this standard, primarily due to utilizing the artificial light source in the UV-spectrometer device.

The Energy Gap Of Sunscreens.

The energy gap in sunscreens refers to the wavelengths of light that the active ingredients of sunscreens can absorb to protect the skin from harmful ultraviolet (UV) radiation. Sunscreens typically contain organic or inorganic compounds that absorb UV light, converting it into less harmful energy, such as heat, it prevents the UV radiation from penetrating the skin and causing damage. Figure 13 illustrates the absorbance spectrum for the samples. The collected data were utilized to determine the band gap energy of the sunscreens. Tauc plots were used to calculate the energy gap of samples. There are many methods for calculating the energy gap, and the subsequent conventional relationship for semiconductor near-edge optical absorption(Haryński et al., 2022):

Where A is a constant, Eg is the material band gap, and n is a quantity equal to 1/2 for a direct band gap and 2 for an indirect band gap compound. Plotting (αh)² vs. hυ yields the energy band gap from absorption spectra. The band gap energy is calculated by extrapolating the straight line to the (αhυ)² = 0 axis.

Figure 8 shows the calculated direct band gap values for all sunscreen samples. The data is tabulated in Table 4. These findings indicated that samples S2, S3, S5, and S6 have a maximum absorption for UV spectrum at corresponding wavelengths 353 nm, 339 nm, 371 nm, and 316 nm, while the samples S1, S4, S7, and S8 have high absorption at corresponding wavelengths 424 nm,454 nm, 402 nm, and (476, 576 nm) that lays the visible spectrum radiation. According to U.S. Food and Drug Administration (FDA) rules, to be labeled as broad spectrum, a product must have a critical wavelength of at least 370 nm, meaning 90 percent of the product’s total absorbance must be at or above this value when measuring from 290 to 400 nm.

The energy gap of a sunscreen typically refers to the energy range within which sunscreen molecules can absorb ultraviolet (UV) radiation effectively, preventing it from penetrating the skin and causing damage. Sunscreens primarily absorb UV radiation in the UVA (320–400 nm) and UVB (290–320 nm) ranges to protect skin from sunburn, premature aging, and skin cancer. When UV photons hit these molecules, they provide just enough energy to bridge this energy gap, causing the molecules to absorb the UV radiation and enter an excited state instead of allowing the energy to reach the skin. Sunscreens are formulated to maintain the stability of the energy gap, as repeated exposure to UV light can degrade certain molecules, reducing their effectiveness. Stabilizers and additional antioxidants are often added to formulas to preserve this energy gap and ensure prolonged protection.

Figure 8: The band gap energy (Eg) of the samples.

CONCLUSION

The UV spectrophotometry method is proposed for the in vitro determination of SPF values and physical properties in cosmetic formulations, particularly sunscreens. This method is simple, fast, and cost-effective, utilizing inexpensive reagents. It measures the spectral transmittance and absorbance of sunscreens in the UV region. The resulting spectral absorbance data predict in vitro SPF values based on standard erythema and solar exposure data. In this study, the calculated SPF values for several sunscreen formulations available in Kurdistan were compared with their labeled SPF values. The results showed that 25% of the analyzed samples closely matched the labeled SPF, 12.5% had SPF values higher than labeled, and 62.5% had SPF values lower than labeled. These findings suggest that a significant proportion of sunscreens used in Kurdistan may offer less protection than claimed, possibly due to the lower cost of these products. Additionally, the UVA/UVB ratio was calculated for all samples, revealing values below 3. This ratio is essential in determining whether sunscreen provides broad-spectrum protection, effectively shielding against UVA and UVB radiation. Broad-spectrum sunscreens help reduce the risk of immediate sunburn (from UVB rays) and long-term skin aging and cancer (from UVA rays). The study also evaluated the energy gap of the sunscreen samples, showing that some exhibited high absorption in the UV spectrum (>400 nm), others absorbed more in the visible spectrum (<400 nm). These wavelengths correspond to the active ingredients in sunscreens, which absorb and protect the skin from harmful UV radiation. The percentage protection factors of products were also compared. The estimated percentage protection SPF factors of tested products is low. A refractive index of products was investigated. The finding was close to one suggesting a transparent appearance and the highest refractive indexes observed were 2.142 for sample S3 and 2.144 for sample S4. This parameter contributes to the SPF by enhancing the scattering and absorption properties and is crucial in ensuring that the sunscreen formulation remains stable and homogenous. Overall, the proposed UV spectrophotometry method proves to be an effective and efficient way to assess SPF values in sunscreen products. These findings hold significant public health implications, particularly given the discrepancies between labeled and actual SPF values.

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Samples		S1	S2	S3	S4	S5	S6	S7	S8
SPF	Label	15	50	50	50	50	60	80	100
SPF	computed	12	36.86	43.84	50.76	49.76	50.25	65	60
Computed relative index UVA/UVB ratio		0.949	2.715	2.620	2.469	2.470	0.755	1.88	2.48

Samples& SPF	S1 15	S2 50	S3 50	S4 50	S5 50	S6 60	S7 80	S8 100

Label percentage %	93.33	98	98	98	98	98.33	98.75	99
Estimated percentage %	91.66	97.28	97.71	98	97.99	98	98.46	98.33

SPF	SPF15	SPF50				SPF60		SPF80	SPF100
samples	S1	S2	S3	S4	S5		S6	S7	S8
Energy gap/eV	2.92	3.52	3.65	2.73	3.34		3.92	3.08	2.6 2.15