WHITE PAPER SUN CARE
However, if these two UV filters must be used together then there are things that can help.
A good method would be to use a chelating agent in the formulation to help avoid complexation.
It is also recommended to use an organic compatible TiO2
such as grades with dense silica coatings. This is because silica is selected as having the lowest potential to interact with BMDM.
Also, using an aqueous TiO2 dispersion means that there is
no interaction with organic UV filters, which allows more optimisation of the oil phase meaning you can really take advantage of the formulation synergy. It should, however, be considered and noted that the combination of BMDM and TiO2
FDA’s proposed rules for sunscreen products is not permitted.
An internal study demonstrated that the yellowing seen when TiO2
is used with BMDM is far less when aqueous TiO2 dispersion is used compared with the oil-based TiO2 dispersion of the same particle size.
This test was performed using a colorimeter after one day, one week and one month. Figure 4 shows the yellowing results when assessed (the higher the b-value the greater the extent of the yellowing).
As you can see in figure 4, there is a clear reduction in yellowing of a formulation when an aqueous TiO2
dispersion
is used alongside BMDM compared with the oil based TiO2 dispersion.
Again, this is thought to be down to the filters working well together as they are in separate phases of the emulsion.
WHAT CAN WE CONCLUDE?
The theory behind synergy is that when organic and inorganic UV filters are combined these UV filters provide two different mechanisms of protection rather than one (if used alone). With an inorganic physical UV filter such as TiO2
, the
mechanism of protection is generated through three mechanisms which are reflection, scattering and absorption of the UV light.
These inorganic filters have many advantages, such as broad spectrum protection, photostability and known mildness. With an organic UV filter, the mechanism of protection is through a chemical reaction that occurs which is initiated
Figure 3 Increase in the optical pathway of photons in an absorbing medium on account of scattering
when UV light hits the UV filter. When this happens there are conformational molecular changes that happen, which are then released as both heat energy and radiation of a high wavelength.
Organic UV filters may have some disadvantages, such as a narrower spectrum of protection along with lower photostability, which is why it can be beneficial to combine with inorganic UV filters. However, when both UV filters are used together, both mechanisms of protection are initiated leading to a synergy effect due to the physical protection mechanisms of the inorganic UV filters along with the absorption mechanisms of the organic UV filters, thus leading to more UV radiation being absorbed and reflected than if the products were used alone. In summary, it is useful to use a combination of organic and inorganic UV filters as TiO2
provides a broad spectrum
base upon which to build. Organic UV filters are then used to build SPF and meet various regional requirements for UVA.
The synergistic effect between inorganic and organic UV filters is beneficial in that it helps to achieve higher SPF and UVA but also gives a lower cost-per-unit of active, which also means that this can be a cost-effective method of formulating high SPF sunscreens.
In addition to this, it is beneficial to use the synergy benefits of a combination of organic and inorganic UV filters as this allows for a higher solids loading within a formulation if the two types of UV filters are used in separate phases.
There are numerous methods of incorporating a combination of both types of UV filters into a formulation. However, the most effective method of incorporation is to use an aqueous dispersion of TiO2 organic UV filters
alongside oil soluble
Author Bethan Spruce, Croda Aline Souza, Croda
www.croda.com
References Full references for this article can be found at
cosmeticsbusiness.com
24 December 2020
cosmeticsbusiness.com ,
Figure 4 TiO2
dispersions and BMDM in an o/w formulation over time
in the US under the current
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