Actives
- The use of phospholipids can significantly increase skin penetration of both oil and water-soluble actives. Examples include lysolecithin and hydrogenated lecithin or phosphatidyl choline.
- Glyceryl caprylate (90% mono) may be useful as a mild, well-tolerated skin penetration enhancer.
- Hydration can significantly improve the skin penetration of actives. The use of synergistic humectant blends combined with lamellar liquid crystal based emulsion systems can provide superior, sustained hydration.
- The optical form of an active can have different biological activity. When using panthenol in formulations you should use the D not DL or racemic form which is only has 50% of the activity of D panthenol. The (-) alpha form of bisabolol is also significantly more effective than the synthetic racemic form.
- Neutralizing lactic or glycolic acid with arginine can reduce skin irritation without reducing its skin exfoliating activity.
- The best nonirritating active to increase cell turnover is n acetyl glucosamine. Increasing cell turnover also helps increase skin lightening and wrinkle reduction efficacy of actives.
- Niacinamide is the most useful and credentialed active ingredient currently available. Niacinamide works synergistically to boost the efficacy of most skin care actives. Examples include combined with n acetyl glucosamine or hexyl resorcinol for skin lightening or combined with tetrahydrodiferuloylmethane for wrinkle reduction.
- When using niacinamide in formulations, use a grade that has less than 100 ppm of nicotinic acid as an impurity. Nicotinic acid is a strong skin irritant.
- Use combinations of actives that work by different or complementary mechanisms to get better skin repair efficacy.
- Niacinamide and polar emollients like PPG 15 stearyl ether can be useful to reduce retinol-induced skin irritation.
- .5% bakuchiol, a retinoid mimic, was shown in a peer reviewed article to provide similar skin benefits as .5% retinol without skin irritation.
- Salicylic should be formulated at a PH of 3 for maximum effectiveness.
Preservation
- Use .5-1% pentylene glycol, hexanediol, ethylhexyl glycerin, or caprylyl glycol to reduce formulation preservative levels.
- All preservatives and potentiators (chelators, pentylene glycol, hexanediol, ethylhexyl glycerin, or caprylyl glycol) should be added to lamellar gel network-based formulations below 45C to insure that they remain mostly in the free bulk water phase of the emulsion for maximum preservation activity.
- Glyceryl caprylate (90% mono) is a preservative that has less negative impact on the viscosity of oil-in-water based lamellar based emulsions than caprylyl glycol, benzyl alcohol, or phenoxyethanol. It also may have less neurosensory types of skin reactions.
- The use of biodegradable chelants like sodium phytate and tetra sodium glutamate diacetate can reduce preservative level by up to 50%. Typical active use levels are .05-.1%.
- The least irritating or sensitizing preservative currently available is probably colloidal silver or silver citrate. The use of chelants should be avoided when using any silver-based preservative.
Hair Conditioners
- Behenyl-based surfactants are the best currently available hair conditioning actives for cream rinse formulations. Examples include behenyl trimethyl ammonium chloride and behenamidopropyl dimethyl amine acid neutralized.
- Using a rinse-off hair conditioner prior to shampooing provides better hair conditioning and volume.
Shampoos/Body Washes
- Use cationic polymers to reduce skin irritation and improve the foam and lather quality of the formulation. Examples include guar hydroxypropyltrimonium chloride and starch hydroxypropyltrimonium chloride. Typical use levels are .2-.5% on an active basis.
- Typical base formulations normally contain ~15% active surfactant comprised of a primary anionic surfactant (7.5-10% active) and amphoteric secondary surfactant (5-7.5% active). Recommended primary surfactants include sodium laureth 1 or 2 sulfate, sodium lauroyl methyl isethionate, or sodium cocoyl glycinate. Amphoteric surfactants play a critical role in thickening the formulation, improving lather, and mildness. Recommended amphoterics include cocamidopropyl betaine, coco betaine, and lauryl hydroxysultaine.
- Humectants that may be useful for improving body wash skin moisturization from include hydroxypropyl bis-hydroxyethyldimonium chloride, sodium polyaspartate, and betaine.
Lipsticks
- The most common waxes used to make lipsticks are ozokerite, carnauba, candelilla, beeswax, microcrystalline, and polyethylene.
- Fumed silica can significantly improve lipstick payoff, color uniformity, stability, and wear time. It can also help prevents lipstick color migration or ‘feathering’ into the fine lines of the lips.
- Using low molecular weight emollients in lipsticks can cause feathering due to their tendency to rapidly spread on skin.
- Adding small amounts of polyethylene wax to lipsticks can be useful to increase the hardness and melting point of sticks without impacting payoff.
Sunscreen formulations
- Formulations containing avobenzone should always contain a biodegradable chelator like sodium phytate or tetra sodium glutamate diacetate to reduce discoloration. Avobenzone forms highly colored complexes with many trace metals. Typical active use levels are .05-.1%.
- Emollients like butyloctyl salicylate and tridecyl salicylate can significantly increase SPF.
- Ethylhexyl methoxycrylene increases SPF more effectively than using octocrylene. It also dissolves avobenzone better.
- Powdered zinc oxide incorporated into the oil phase of formulations should use polyhydroxystearic acid or polyglyceryl 6 polyricinoleate as dispersing agents. The recommended level is 5-10% based on the % zinc oxide used.
- Zinc oxide/titanium-based formulations should have in vitro SPF testing performed on stability samples
- Always age zinc oxide/titanium-based formulations several weeks before submitting for in vivo SPF testing. SPFs can be lower by up to 20% after several weeks of aging.
Miscellaneous
- My recommended stability protocol for testing emulsions
- 1 month at 50C
- 3 months at room Temperature, 5C, and 45C
- Freeze thaw cycle (-15C to RT)
- Centrifugation (3000 rpm for 20 min)
- Vibrating table (400 rpm for 4 hours)
- The best predictive way to judge if an emulsion is heat stable is to measure the viscosity hot at whatever your upper stability temperature is
- Silicone resins (polymethylsilsesquioxane) are good at reducing the tacky feel of formulations and providing a soft-focus wrinkle blurring effect on skin. Silicone resins also can have skin exfoliating effects when rubbed on skin due to their abrasively.
- Dimethicone can reduce the soaping of oil-in-water emulsions when rubbed on skin. Typical use levels are 1% of a 5 or 10 cts. dimethicone.
- Always use dispersing agents when incorporating large amounts of powders/pigments into either the water or oil phase of formulations. Examples include polyhydroxystearic acid or polyglyceryl 6 polyricinoleate for oil dispersions and sodium polyacrylate for water dispersions.
For more information, please refer to Part One
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How does testing the viscosity test the heat stability of an emulsion?
Thank you very much for all these tips George, really useful!
Can I ask if you know a natural equivalent of dimethicone for reducing the soapiness of emulsions please?
Dear Lindsey,
The key for getting good hot emulsion stability is for the product to have enough viscosity and yield value to prevent droplet coalescence. If an emulsion is viscous at elevated temperature it is unlikely to separate. I like to compare the hot viscosity with the room temperature viscosity.
Thanks for reading!
George
Dear Pauline:
There are no natural alternatives that work as well as Dimethicone.
Thanks for reading,
George
Hello George. This is Great Post! Thank you for sharing the information.
One Quick Question. When you say Maximum efficacy of Salicylic Acid at pH 3, you mean for Efficacy against Acne correct?
Also, how does some State Regulations affect when it comes to pH at 3.0 ? Most of the Regulations allow pH between 3.5-4.5. Can you please throw some light on that?
Dear Nirmal:
The PkA of Sal acid is 2.9 which means that it is 50% ionized at that PH. This is an optimum PH for anti-acne efficacy since at higher PHs Sal acid skin penetration goes down. I’m not aware of any state regulations that restrict the PH of Sal acid containing products to a PH of greater than 3.5.
Thanks for reading!
George
Hi George,
I am currently formulating SPF 50 Mineral c-spray BOV. Tio2 and ZnO are uncoated. Formula is stable, spray is very good. The issue is Initial pH was 6.8 and moved into 7.2 after 24 hrs. 4 month later pH = 8.8.
My questions are as follows …… 1. how do you control pH? to stop at around pH of 8. 2. what drive the pH high ? 3. what is the right pH for sunscreen products?
Thank you,
suleyman
Dear Suleyman:
The only way of preventing or reducing the Zinc Oxide PH drift is to use a silicone treated grade dispersed in the oil phase of the emulsion.
Thanks for reading!
George