SPF Boosters

Image: Credit link

There are some ingredients on the market that aren't approved sunscreen actives but boost SPF. One of these such ingredients is butyloctyl salicylate. Butyloctyl salicylate is an emollient that absorbs UVB. It can boost SPF like organic UVB sunscreen active. Canada limits butyloctyl salicylate to 5% in sunscreens. In addition there a blends of antioxidants that can boost SPF as well as UVA protection. These blends are great because in addition to boosting SPF and UVA protection, one can claim antioxidant benefit on the sunscreen label. Which consumer doesn't love antioxidants?! These SPF boosters are great for cases when you are almost at your target SPF but just need an extra boost to reach your target or surpass it.

ZnO and TiO2 Dispersions

Image: Credit link

A dispersion is a system in which particles are dispersed in a continuous phase of a different composition. A dispersion can consist of 4 variables: pigment, surface coating, dispersant, and vehicle. For the pigment, we will focus on ZnO and TiO2 in this post. Attention must be made to the primary particle size of the ZnO and TiO2. You do not want it to be too large. The surface coating reduces aggregation and reduces oil absorption so that the dispersion flows and is not chunky. The dispersant improves wetting and stabilizes the suspended particle. The vehicle provides a medium and wets the particulate.

Dispersions are great to use because they are so convenient. It is so much easier to just put the dispersion into your formula instead of making grinds. The particle size in the dispersion is made to the ideal size so you will get better results on your SPF and UVA testing. In addition, there will be better transparency in the finished sunscreen formula because of the small particle size in the dispersion. Dispersions help cut labor and enhance skin feel. I love to use dispersions!

Transmittance vs Absorption Curve

Sometimes you will see transmittance of absorption curves to show the UVA and UVB protecting abilities of a sunscreen active. Transmittance is the fraction of incident light at a specified wavelength that passes through a sample. In other words it measures the amount of wavelength that goes through. You want the transmittance to be low for a sunscreen active because that shows that low amounts of wavelength are passing through the sunscreen active. We want UVA and UVB to be absorbed and scattered, not to pass through and penetrate our skin. The transmittance curve below is that of a ZnO sunscreen. We see fairly low transmittance of UVB and UVA radiation. On the other hand, we see a high transmittance of visible light which is showing that ZnO is not very whitening. If ZnO scattered a large amount of visible light then it would be very whitening and ashy looking on the skin.

Typical UV protection provided by ZnO Sunscreen Credit Link

If we flip this curve, we get an absorption curve which is the opposite of a transmittance curve. An absorption curve shows the amount of wavelength being absorbed, not transmitted. For a sunscreen active, we want a high amount of absorption of UVA and UVB radiation because that shows it will not penetrate the skin and cause damage.

Transmittance and absorption curves are important to understand the UVA and UVB protecting of the sunscreen actives that you will be working with.

TiO2 and ZnO Powders

Image: Credit link

I am going to focus again on zinc oxide and titanium dioxide. These inorganic sunscreens come in a powder (particulate) form. Their particle size is very important. The smaller the particle size, the better the UVB protection, hence higher SPF. This is the result of a higher level of surface area which is scattering UV radiation. However, the smaller the particle size, you will lose some of the UVA protection. There is an optimum particle size for in vivo PFA testing. For a critical wavelength of 370nm or above, which is an in vitro test, you want a bigger particle size to provide more blocking (create a film on the skin).  But be careful, because as you get bigger you will be more whitening. Therefore, it is best to choose a particle size that is mid-range, not too small and not too big for both UVB and UVA protection or two use a combination of TiO2 and ZnO.

You can incorporate TiO2 and ZnO in a powder form into your sunscreen formulation. If is is untreated it is naturally hydrophilic and it will go into the water phase. However, it is beneficial to surface treat these powders so that they can be easily incorporated into the oil/silicone phase of your formulation, and also to avoid problems with zinc oxide and pH. W/O emulsions are more efficient for SPF because it leaves a thicker film. Surface treatment can either make TiO2 and ZnO hydrophobic (water hating) and/or lipophillic (oil loving). The sunscreen actives will then be in the oil or silicone phase and not be washed off easily when you come in contact with water.  Making a water in silicone sunscreen is especially nice because W/Si does better with water resistance. For a water in silicone sunscreen, you want to make sure that the sunscreen active is surface treated so that it is hydrophobic. Surface treatment is also beneficial because it will prevent unwanted chemical reactions between the untreated TiO2 or ZnO and the other ingredients in your formula. Additional, small sized TiO2 gets a grayish blue color when exposed to UV light and to prevent this color change a surface treatment of alumina on the TiO2 is extremely helpful.

It is important to note that TiO2 and ZnO are not supplied as primary particle sizes, they are supplied as  aggregates. Aggregates form due to the high surface energy of the primary particles and charges making the primary particles stick together. Furthermore, agglomerates can be formed from the aggregates sticking together. Treating TiO2 and ZnO and breaking the agglomerates down during manufacturing creates smaller TiO2 and ZnO which creates a nicer finished formula.

However, if you are using TiO2 and/or ZnO powders you must have the milling equipment to bring the particles down to a very small size, which is difficult. If you have multiple locations where your sunscreen product is being made, do all locations have the same equipment and will the same parameters be used? It is much easier to use TiO2 and ZnO dispersions which already have the particles milled to an ideal size.  Therefore, the dispersions you use will always have the same particle size and hence your product's SPF/UVA testing will be consistent. I will discuss dispersions in my next post.

Organic Sunscreen Actives

Image: Credit Link

Organic sunscreen actives are carbon based hence the name organic. They are also called chemical sunscreen actives. They work using a different mechanism than inorganic sunscreen actives to protect your skin from the UV rays. Organic sunscreen actives absorb UV radiation, dissipating it as heat, rather than deflect and block as do the inorganic sunscreen actives. Organic sunscreen actives are bothersome for some people causing irritation and allergic reactions. The inorganic sunscreens actives are a better choice if you are sensitive to the organics.

Here is a chart showing all of the organic sunscreen actives as well as the inorganic sunscreens (TiO2 and ZnO).  In addition, this chart shows the maximum concentrations allowed in a finished sunscreen product.

UV-filter	Other names	Maximum concentration	Permitted in these countries	Results of safety testing
p-Aminobenzoic acid	PABA	15% (EC- banned from sale to consumers from 8 October 2009)	USA, AUS	Protects against skin tumors in mice.[42][43][44] Shown to increase DNA defects, however, and is now less commonly used.
Padimate O	OD-PABA, octyldimethyl-PABA, σ-PABA	8% (EC,USA,AUS) 10% (JP) (Not currently supported in EU and may be delisted)	EC, USA, AUS, JP	Not tested
Phenylbenzimidazole sulfonic acid	Ensulizole, Eusolex 232, PBSA, Parsol HS	4% (US,AUS) 8% (EC) 3% (JP)	EC,USA, AUS, JP	Genotoxic in bacteria[45]
Cinoxate	2-Ethoxyethyl p-methoxycinnamate	3% (US) 6% (AUS)	USA, AUS	Not tested
Dioxybenzone	Benzophenone-8	3%	USA, AUS	Not tested
Oxybenzone	Benzophenone-3, Eusolex 4360, Escalol 567	6% (US) 10% (AUS,EU) 5% (JP)	EC, USA, AUS, JP	Not tested
Homosalate	Homomethyl salicylate, HMS	10% (EC, JP) 15% (US,AUS)	EC, USA, AUS, JP	Not tested
Menthyl anthranilate	Meradimate	5%	USA, AUS	Not tested
Octocrylene	Eusolex OCR, 2-Cyano-3,3-diphenyl acrylic acid, 2-ethylhexylester	10%	EC,USA, AUS, JP	Increases ROS[46]
Octyl methoxycinnamate	Octinoxate, EMC, OMC, Ethylhexyl methoxycinnamate, Escalol 557, 2-Ethylhexyl-paramethoxycinnamate, Parsol MCX	7.5% (US) 10% (EC,AUS)20% (JP)	EC,USA, AUS, JP
Octyl salicylate	Octisalate, 2-Ethylhexyl salicylate, Escalol 587,	5% (EC,USA,AUS) 10% (JP)	EC,USA, AUS, JP	Not tested
Sulisobenzone	2-Hydroxy-4-Methoxybenzophenone-5-sulfonic acid, 3-Benzoyl-4-hydroxy-6-methoxybenzenesulfonic acid, Benzophenone-4, Escalol 577	5% (EC) 10% (US, AUS, JP)	EC,USA, AUS, JP
Trolamine salicylate	Triethanolamine salicylate	12%	USA, AUS	Not tested
Avobenzone	1-(4-methoxyphenyl)-3-(4-tert-butyl phenyl)propane-1,3-dione, Butyl methoxy dibenzoylmethane, BMDBM, Parsol 1789, Eusolex 9020	3% (US) 5% (EC,AUS)10% (JP)	EC, USA, AUS, JP	Not available[47]
Ecamsule	Mexoryl SX, Terephthalylidene Dicamphor Sulfonic Acid	10%	EC,AUS (US:Approved in certain formulations up to 3% via New Drug Application (NDA) Route)	Protects against skin tumors in mice[48][49][50]
Titanium dioxide	CI77891	25% (No limit Japan)	EC,USA, AUS, JP	Not tested
Zinc oxide		25% (US) 20% (AUS) (EC-25% provided particle size >100 nm) (Japan, No Limit)	EC,USA, AUS, JP	Protects against skin tumors in mice[48]

Image: Credit link

There are also several other sunscreen actives that are not approved for use in the US but are approved else where. Most of these sunscreen actives are for UVA protection. 

UV-filter	Other names	Maximum concentration	Permitted in
4-Methylbenzylidene camphor	Enzacamene, Parsol 5000, Eusolex 6300, MBC	4%*	EC, AUS
Tinosorb M	Bisoctrizole, Methylene Bis-Benzotriazolyl Tetramethylbutylphenol, MBBT	10%*	EC, AUS, JP
Tinosorb S	Bis-ethylhexyloxyphenol methoxyphenol triazine, Bemotrizinol, BEMT, anisotriazine	10% (EC, AUS) 3% (JP)*	EC, AUS, JP
Neo Heliopan AP	Bisdisulizole Disodium, Disodium phenyl dibenzimidazole tetrasulfonate, bisimidazylate, DPDT	10%	EC, AUS
Mexoryl XL	Drometrizole Trisiloxane	15%	EC, AUS
Benzophenone-9	Uvinul DS 49, CAS 3121-60-6, Sodium Dihydroxy Dimethoxy Disulfobenzophenone [53]	10%	JP
Uvinul T 150	Octyl triazone, ethylhexyl triazone, EHT	5% (EC, AUS) 3% (JP)*	EC, AUS
Uvinul A Plus	Diethylamino Hydroxybenzoyl Hexyl Benzoate	10% (EC,JP)	EC, JP
Uvasorb HEB	Iscotrizinol, Diethylhexyl butamido triazone, DBT	10% (EC) 5% (JP) *	EC, JP
Parsol SLX	Dimethico-diethylbenzalmalonate, Polysilicone-15	10%	EC, AUS, JP
Isopentenyl-4-methoxycinnamate	Isoamyl p-Methoxycinnamate, IMC, Neo Heliopan E1000, Amiloxate	10% *	EC, AUS

Image: Credit link

Here is a chart showing the UVB and UVA protection ability of sunscreen actives. You will see that Zinc Oxide protects against both UVB and UVA radiation. 

Image: Credit link

PABA is very irritating and is not used much anymore. In the USA, TiO2 and ZnO cannot be used with avobenzone. If you do work with avobenzone be aware that it can make the sunscreen yellow. TiO2 reacts with avobenzone and makes the formula yellow.