The New Sunscreens among Formulation Strategy, Stability Issues, Changing Norms, Safety and Efficacy Evaluations
- Do not stay too long in the sun, even while using a sunscreen product.
- Keep babies and young children out of direct sunlight.
- Over-exposure to the sun is a serious health threat.
- Reducing the quantity of sunscreen product applied will significantly lower the level of protection.
- Apply (generously) sunscreen products before sun exposure.
- Reapply frequently to maintain protection, and especially after perspiration, swimming or towelling.
- Ensure uniformity of skin application, resistance to water, sweat and lately, the abrasive action of the sand;
- Be photo-stable, in order to preserve the UV filters from the decomposition induced by solar irradiation and, consequently, the loss of efficacy during the period of the consumer exposure;
- Reach the right synergic combination targeted for normal skin, sensitive skin and babies consumers, able to avoid all skin sensitization or photosensitization;
2. Efficacy and Evaluation of UVB Sunburn Protection Factor (SPF)
3. Evaluation of the Sun Product Water Resistance
4. In Vitro Determination of UVA Photoprotection
5. Further In Vitro/In-Vivo Methods
6. FDA 2011 Final Rule
- the calibration times of the UV source (each 12 months for the FDA, each 18 months for the ISO);
- the reference sunscreen products (P2 for the FDA and P2, P3 or P7 for the ISO);
- progressions of exposure times used.
- 40 min water resistance followed by the SPF value measured after the immersion
- 80 min water resistance followed by the SPF value measured after the immersion
7. Australia Sunscreen Standard AS/NZS 2604:2012
- LOW protection: 4-6-8-10
- MEDIUM protection: 15-20-25
- HIGH protection: 30-40-50
- VERY HIGH protection: 50+
- SPF from 4 to 7: no water resistance properties
- SPF from 8 to 14: maximum 40-min water resistance properties
- SPF from 15 to 29: maximum 2-h water resistance properties
- SPF > 30: maximum 4-h water resistance properties
8. Formulation Solutions
- Diethylamino Hydroxybenzoyl Hexyl Benzoate and Ethylhexyl Triazone in 3:1 ratio ;
- Octocrylene and Butyl Methoxydibenzoylmethane in a ratio of more or less 3:1 ;
- Octocrylene + Butyl Methoxydibenzoylmethane + Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine ;
- Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine (Bemotrizinol) + Diethylhexyl Butamido Triazone + Butyl Methoxydibenzoylmethane (based on our experience, unpublished data).
- The right stabilizers:
- Among other filters (Octocrylene, Polysilicone-15, Methylbenzylidene Camphor, Bemotrizinol, etc.);
- among antioxidants (Pentaerythrityl tetra-di-t-butyl hydroxyhydrocinnamate, Diethylhexyl Syringylidenemalonate);
- Solubility: octocrylene, ethylhexyl and homomenthyl salicylates, to avoid crystal formation;
- Avoiding the incompatibility with metal ions, by using chelating agents like Disodium EDTA
- Avoiding formaldehyde donors;
- The combinations of Avobenzone with inorganic UV filters (this is not allowed in the USA) can improve the stability of avobenzone by about 10–15% but the inorganic UV filters must be of the coated type;
- Use polar solvents to inhibit Norrish-Type-I cleavage of Avobenzone (Paraffin is bad, Ethanol is good);
- The type of final users. The use of Octocrylene, Ethlylhexyl Methoxycinnamate and PABA derivatives is not suggested for consumers with sensitive skin or for baby products .
- The market: Europe, Japan, USA, etc., similarly to what happens for test methods, also the number of available sunscreen ingredients is different according to the different legislations. In USA (where sunscreen products are sold as OTC and not as cosmetic products) the available number of UV filters is extremely limited in comparison to Europe. Also their maximum allowed percentages are in many cases different (Ethlylhexyl Methoxycinnamate allowed at 10% in Europe, at 20% in Japan);
- If a water resistant formula is requested, the use of hydrosoluble UV filters (Phenylbenzimidazol Sulfonic Acid) could be a bad idea;
- Preparing a fully anhydrous formulation with the addition of film forming polymers;
- Creating w/o emulsions;
- Obtaining a meta-stable o/w emulsion with a low level of emulsifiers, adding, also in this case, good film forming polymers;
Conflicts of Interest
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|Protection Level||SPF Value|
|Low protection||6, 10|
|Medium protection||15, 20, 25|
|High protection||30, 40|
|Very high protection||50+|
|Country||SPF Method||ISSUE DATE|
|USA *||FDA||1978 (‘93)|
|Type 1||always burns, never tans|
|Type 2||usually burns, tans with difficulty|
|Type 3||sometimes burns, sometimes tans|
|Type 4||burns minimally, always tans|
|Type 5||rarely burns, tans profusely|
|Type 6||never burns, deeply tans|
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Lionetti, N.; Rigano, L. The New Sunscreens among Formulation Strategy, Stability Issues, Changing Norms, Safety and Efficacy Evaluations. Cosmetics 2017, 4, 15. https://doi.org/10.3390/cosmetics4020015
Lionetti N, Rigano L. The New Sunscreens among Formulation Strategy, Stability Issues, Changing Norms, Safety and Efficacy Evaluations. Cosmetics. 2017; 4(2):15. https://doi.org/10.3390/cosmetics4020015Chicago/Turabian Style
Lionetti, Nicola, and Luigi Rigano. 2017. "The New Sunscreens among Formulation Strategy, Stability Issues, Changing Norms, Safety and Efficacy Evaluations" Cosmetics 4, no. 2: 15. https://doi.org/10.3390/cosmetics4020015