SPF boosters are ingredients that can significantly increase in vivo SPF but don’t alone contribute meaningfully to SPF. Due to recent Hawaii regulatory actions banning the use of Octinoxate and Oxybenzone in beach products, the need for SPF boosting technologies has never been greater in the US.
Most of the remaining UVB absorbers such as Octocrylene, Homosalate, and Octisalate, are weak UVB absorbers and the only remaining potent UVB absorber, Ensulizole, is water soluble.
Titanium Dioxide is a moderately potent UVB absorber, however it can’t be formulated in combination with Avobenzone and can whiten skin. Additionally, the current trend is high SPF products over an SPF of 50, which means that many formulations are approaching the maximum allowable sunscreen limits.
The average SPF efficiency (SPF/% sunscreen used) of day wear photo protecting products sold in the US using organic sunscreens is only around 1.8 and beach products 2.5. Titanium Dioxide/Zinc Oxide based sunscreens are higher with an efficiency of ~3.0 (Zinc Oxide only ~1.5). The average SPF efficiency of chemical sunscreen formulations in the last 40 years has only increased from ~1-2 to ~2-3 SPF units/1% sunscreen.
This means that a typical day wear SPF 30 product may contain 17% organic sunscreen and a beach product 12%. A good SPF booster can significantly increase this SPF efficiency by ~50-200% depending on the base formulation and types of sunscreens used. This would reduce the sunscreens needed from 17% to 8.5-11.3% for day wear products and 6-9.6% for beach products.
The normal use level of SPF boosters in formulations is 1-3% on an active basis and most work primarily by increasing UV absorption and the sunscreen film thickness on skin. Other mechanisms of action include:
- increasing the UV scattering ability of sunscreens
- increasing the UVA coverage by extending the critical wavelength
- improving the UV stability of sunscreens
- reducing UV induced skin erythema
The formulation challenge is to get good SPF boosting activity while not compromising on skin feel.
The various types of SPF boosters currently used include:
- oil soluble and hydrophilic polymer solutions
- polymeric dispersions/powders (polyurethanes or polyacrylates)
- emollients
- waxes
- cosmetic soothing agents
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Oil soluble and hydrophilic polymers function mainly by film formation, causing an increase in the UV absorption by increasing the optical path length or film thickness on skin. Doubling the optical path length or film thickness will result in a doubling of the SPF.
Polymeric and non-polymeric waxes can also form solid sunscreen containing particles in oil in water emulsions that can increase UV absorption and scatter, which also can increase the optical path length.
Emollients are mainly used to help dissolve crystalline sunscreen like Avobenzone or Oxybenzone, extend UVA coverage by increasing the critical wavelength, and help improve Avobenzone photostability.
Many SPF boosters can provide additional benefits such as improving the wash/wear resistance of formulations and reducing sunscreen skin penetration. This is becoming important since recent research suggests that once sunscreens penetrate skin, they can promote free radical formation in the presence of UV (1). The FDA has also signaled that they are becoming concerned with sunscreen skin penetration (2).
SPF formulation strategies
- Combine SPF boosters that work by different mechanisms
- Hydrophilic polymers combined with oil soluble polymers
- Emollients combined with oil soluble or hydrophilic polymers
- UV scattering agents combined with oil soluble or hydrophilic polymers
- Use multifunctional technologies that can provide SPF boosting effects
- Emollients can solubilize, and help photostabilize Avobenzone
- Many polymers can improve the wear, rub, or wash resistance of formulations
- Preservatives like Caprylyl glycol can help increase SPF
- Chelating agents can prevent formulation discoloration due to Avobenzone reacting with metals and can help with preservation
- Cosmetic soothing agents like Bisabolol and D Panthenol have been shown to increase SPF.
- Commonly used antioxidants like Tocopheryl Acetate have been shown to increase SPF
- Alkylmethylsiloxanes can improve skin feel and increase SPF
- Less is better. Develop efficient systems that work at <2% solids to maintain good skin feel (emollients may be needed at a higher concentration if used to solubilize Avobenzone)
- Reducing the particle size of chemical sunscreens emulsified into oil in water emulsions can significantly increase SPF by as much as 70 percent and improve skin feel
Recommended oil soluble polymers (based on SPF boosting efficiency)
- Bis-Peg-12 Dimethicone Candelillate
- VP Eicosene Copolymer – a historic benchmark
- Tricontanyl/PVP
- C30-38 Olefin Isopropyl Maleate/MA Copolymer
- Bis-Hydroxyethoxypropyl Dimethicone
Recommended hydrophilic polymers (based on SPF boosting efficiency)
- Styrene/Acrylates copolymer is a 350 nm hollow particle that scatters UV. It is one of the most commonly used SPF boosters on the market and works well with metal oxides.
- PVP/Dimethiconylacrylate/Polycarbamyl/Polyglycol Ester
- Acrylates/Methacryloyloxyethyl Phosphate Copolymer – good for metal oxides
Recommended emollients/miscellaneous ingredients (based on SPF boosting efficiency)
- Carthamus Tinctorius (Safflower) Oleosomes (and) Carthamus Tinctorius (Safflower) Seedcake Extract
- C20-40 Alcohols
- Ethylhexyl Methoxycrylene can dissolve ~32% Avobenzone and is an excellent Avobenzone photostabilizer and can increase UVB/UVA protection
- Diethylhexyl 2,6-Naphthalate can dissolve ~18% Avobenzone and is a good Avobenzone photostabilizer/SPF booster
- Phenylethyl Benzoate can dissolve ~24% Avobenzone and can increase the critical wavelength of formulations. Emollients like Butyloctyl Salicylate can also help increase SPF.
References
- University of California – Riverside. “Sunscreens Can Damage Skin, Researchers Find.” ScienceDaily, 29 August 2006.
- Statement from FDA Commissioner Scott Gottlieb, M.D., on new FDA actions to keep consumers safe from the harmful effects of sun exposure, and ensure the long-term safety and benefits of sunscreens, https://www.fda.gov/newsevents/newsroom/pressannouncements/ucm608499.htm
Learn more:
- Developing Superior Sun Care Formulations
- Encourage Skin Care with Sunscreen Sensorial Modifiers [VIDEO]
- Formulating an Emulsifier-Free Sunscreen
- Sunny Days Ahead for Waterproof Enhancing Technologies
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Thank you for sharing a wonderful blog
Thankyou for the info,i just wanna ask how about hydrolyzed wheat protein/PVP crosspolymer does it effective as SPF booster? If it yes,what is the best presentation for SPF 30? Thankyou
Dear Amiravoir:
I think there are better SPF boosters.
Thanks for reading,
George