Protecting the sunscreen

UV filters protect the skin against sunburn and ageing by absorbing the UV light. Therefore, the active ingredients themselves can be damaged by the absorbed energy resulting in chemical degradation. This can reduce the effectiveness of the product, and lead to allergic reactions¹ and endocrine disrupting effects². Therefore, it is necessary to protect the ingredients from damage in the packaging.

Light transmittance

Ultraviolet (UV) rays can pass through the packaging and damage the UV filters for example on the retail shelves, during storage at home near a window or when exposed to direct sunlight. Since the UV radiation in the sunlight ranges from 290 to 400nm (figure 1, p 28), the packaging materials must absorb the radiation almost completely across the entire wavelength spectrum.

Consequently, photoprotective barriers for sunscreen products are essential. To measure the effect of this barrier, light transmittance needs to be studied. Transmittance is defined as the amount of light a material transmits at a particular wavelength. Many plastic materials can reduce transmission of UV-B and -C light4.

For example, Polymethyl methacrylate (PMMA, acrylic glass) is often used for transparent packaging such as jars, powder compacts and lip-gloss tubes and absorbs UV radiation completely only between 200 to 235nm. Polypropylene (PP) behaves similarly and is commonly used for bottles and tubes of cosmetic products. Polyethylene terephthalate (PET) is also a common material for bottles and tubes but shows complete absorption between 200 and 310nm. In addition, increasing age or previous exposure of the material, such as recycling, also affects the absorption of light.

Oxidation reactions and active ingredient degradation can occur due to the UV-A radiation between 280 to 400nm, where these plastics all transmit light. Therefore, an additional barrier is required in this area, where both an organic and inorganic UV filter can be applied. For example, benzo-
phenone absorbers can act as organic additives for plastics, whereas nanoparticles of ZnO, TiO2 and iron oxides are common inorganic substances for this purpose. Incorporating those additives into the plastic might lead to 
disadvantages during recycling. Therefore, their application as coating layer or sleeve to the surface of the packaging can ensure product protection and sustainability, where the thickness of the layer determines the transmission5. Although sun care products are bought more frequently in the sunny seasons, they are available in stores all year round, where they are exposed to halogen lamps with an UV emission around 365nm (figure 2, page 28). By maximising the UV absorption of the packaging, efficient product protection can be ensured even under store lighting⁶.

Oxidation

Oxidation reactions in cosmetic emulsions are substantially accelerated by the influence of light⁷. Therefore, the exclusion of ultraviolet light, e.g., by using effective UV filters in packaging, can support quality retention. Adding antioxidants to the sunscreen may also be helpful⁸. However, it is impossible for an oxidation reaction to occur without oxygen itself. Therefore, the oxygen barrier of the packaging is the safest way to reduce all oxidative changes after the product is filled^9,10. The barrier is related to mobility of the molecular network of the polymer, the density, and intermolecular interactions. The copolymer ethylene vinyl alcohol (EVOH) serves as typical barrier material used as an intermediate layer in tubes, jars, and bottles. Metallisation with aluminium is also a very good barrier regarding gases, moisture, and organic substances. Furthermore, using ceramic layers of ultra-thin silicon oxide may be beneficial. Nanomaterials incorporated in barrier layers are also suitable options. A new trend is moving towards biopolymers, compostable coatings, and the use of natural materials such as paper¹¹, bamboo¹² or cork¹³.

It is important to take into account that different barrier materials might have varying permeabilities for oxygen, water vapour, or aromatic substances. The investigation of the permeability of flat as well as formed packaging materials can be carried out in various ways.

Temperatures

High temperatures also accelerate the oxidation or chemical degradation reactions. On the one hand, the packaging heats up due to the irradiation with infrared light from the sun, and on the other hand, the temperature rises further due to the transformation of UV energy into thermal energy generated by the UV filters. If the product is used in summer, the starting temperature is higher due to the additional heat of the environment. Therefore, it is necessary to take precautions to keep the temperatures low, which develop in the packaging when exposed to light. An example would be the development of a bright or reflective packaging surface to reflect a large portion of the incident solar energy, rather than absorbing it.

The higher temperatures may also lead to physical changes. The barrier properties of the packaging are weakened by the faster diffusion, while the increase in temperature causes pressure to build up inside the packaging. This can lead to the water vapour barrier no longer being adequate¹⁶, resulting in non-compliance with the volume or weight claims on the product or to emulsions becoming unstable due to changed proportions of oil and water phase.

References:

1. Darvay, A., White, I. R., Rycroft, R. J. G., Jones, A. B., Hawk, J. L. M., & McFadden, J. P. (2001). Photoallergic contact dermatitis is uncommon. British Journal of Dermatology, 145(4), 597-601.
2. Wang, J., Pan, L., Wu, S., Lu, L., Xu, Y., Zhu, Y., ... & Zhuang, S. (2016). Recent advances on endocrine disrupting effects of UV filters. International journal of environmental research and public health, 13(8), 782.
3. https://commons.wikimedia.org/wiki/File:Solar_AM0_spectrum_with_visible_spectrum_background_
4. %28en%29.pngMartínez-García, A., Oller, I., Vincent, M., Rubiolo, V., Asiimwe, J. K., Muyanja, C., ... & Polo-López, M. I. (2022). Meeting daily drinking water needs for communities in Sub-Saharan Africa using solar reactors for harvested rainwater. Chemical Engineering Journal, 428, 132494.
5. Springer, A., Reinelt, M., Jesdinszki, M., & Wunderlich, J. How Can the Right Choice of Packaging Materials Prevent a Loss of Quality in Sun Care Products?.
6. Böhner, N., Hösl, F., Rieblinger, K., & Danzl, W. (2014). Effect of retail display illumination and headspace oxygen concentration on cured boiled sausages. Food Packaging and Shelf Life, 1(2), 131-139.
7. Springer A, Ziegler H. The Role of Preservatives and Multifunctionals on the Oxidation of Cosmetic O/W Emulsions. Cosmetics. 2022; 9(3):59.
8. Souza, C., Campos, P. M., Schanzer, S., Albrecht, S., Lohan, S. B., Lademann, J., ... & Meinke, M. C. (2017). Radical-scavenging activity of a sunscreen enriched by antioxidants providing protection in the whole solar spectral range. Skin pharmacology and physiology, 30(2), 81-89.
9. Piringer, O. G., & Baner, A. L. (Eds.). (2008). Plastic packaging: interactions with food and pharmaceuticals. John Wiley & Sons.
10. Robertson, G. L. (2012). Introduction to food packaging. Food Packaging: Principles and Practice, 3rd ed.; CRC Press, Taylor & Francis Group: Boca Raton, FL, USA, 1-8.
11. https://www.neue-verpackung.de/pharma-kosmetik/papier-primaerverpackungen-fuer-kosmetika-545.html
12. https://www.interpack.de/de/Entdecken/Tightly_Packed_Magazin/Kosmetikverpackungen/News/Nachhaltig_verpackt
13. https://www.neue-verpackung.de/markt/70-prozent-kork-100-prozent-recycelbar-98.html
14. https://www.ivv.fraunhofer.de/en/packaging/permeation-analysis.html
15. Rosenow, Phil; Destler, Elisabeth; Springer, Arielle. The Search for Suitable Packaging for Cosmetics – a Case Study. Sofw Journal (2022), Nr. 10, 5 S. 60-63
16. Langowski, H. C. (2008). Permeation of gases and condensable substances through monolayer and multilayer structures. Plastic packaging: interactions with food and pharmaceuticals, 297-347.