Sunscreens – The ultimate preservative challenge

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Sunscreen products are known as a challenge in terms of preservation. The unique composition and features which are inherent to sunscreen formulations such as high organic phase vs water ratio, as well as the presence of specific UV filters, introduce much complexity to the preservation process.

Broad spectrum skin protection

An optimum sunscreen formula should first and foremost provide broad spectrum skin photoprotection against the detrimental effects of sun exposure. However, as a cosmetics product, it should also hold sensorial appeal at an affordable price to the consumer.

Blending various UV filters

Sunscreen can be classified depending on their mode of action, primary protective elements – UV filters absorb, reflect or scatter harmful UV rays from penetrating the skin. Blending of various UV filters at low percentages is often preferred over a combination of 2 or 3 of them at high dosage, for reasons of safety and to achieve synergistic effect for wider spectrum protection. Processing oily-soluble UV filters into a stable fine emulsion, dictates the use of a higher dosage of solubilizers and humectants, resulting in a significantly higher oily-phase formula.

Sensitive balance is a key

The use of components such as antioxidants & osmolytes, provides a secondary protective factor to counteract the inherent photochemical processes triggered by UV-penetration, that can induce DNA damage in the skin cell. The essence of assembling a successful sunscreen formula lays in the sensitive balance of such complexity.

The Ideal Polarity Index

Each molecule has a polarity value that can be scaled in many ways. One of the most popular polarity scale is the LogP (Partition coefficient).

Preservatives also have a LogP value that can anticipate their distribution in a cosmetic emulsion.
Non-polar preservatives (LogP >1) will have a tendency to migrate into the organic phase, therefore, deserting the water phase – i.e. the scene of the antimicrobial activity.

Sharon Laboratories are presenting SharoSUN™: a preservative solution platform with an ideal polarity index to feet high SPF formulations, providing broad spectrum protection at a low level of use. This platform is free-from parabens, formaldehyde donors and Phenoxyethanol.

We encourage you to contact our experts to learn more and to choose together the best preservative solution for your sunscreen formulation.

Written by Mrs. Julie Soffer, Global Technical Expert

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