A ‘healthy’ tan or summer glow is often desirable for Caucasian skin types but with the dangers of UV light and traditional tanning, the use of self-tanning products has become more popular than ever. Not only restricted to the summer season, tanning agents are commonly used throughout the year to achieve a golden or bronzed skin tone for special occasions where a little bit of extra skin will be seen. As competition heats up to provide consumers with the perfect ‘natural’ tan they are looking for – especially with so many products already on the market – the question is how to get a deeper, browner, faster, more natural and more even tanning result from the next self-tanning development. There are several key features to bear in mind in order to obtain a great tanning product. Belinda Carli from the IPCS explains how to develop new self-tanners with essential elements.
Self-tanning basics: understanding DHA and incompatibilities
Dihydroxyacetone (DHA) is the most popular material used in tanning products today. It was ‘accidently’ discovered to cause a temporary tanning colour to the skin through food and medical use in the early 1900’s. However, experimentaion in self-tanning products took some time to come into fruition; the first commercial products weren’t launched until the 1960’s. DHA creates colour through a similar process to the Maillard reaction: a chemical reaction between amino acids and reducing sugars that in preparing foods gives a baked golden brown appearance and adds to aroma and flavour. When used in personal care products, DHA reacts with amines, peptides and amino acids of the stratum corneum to produce brown polymers called melanoidins which have a similar colour to the skins natural production of melanin when produced to UV light, see fig. 1. The use of DHA on the skin unfortunately also leaves a very distinctive smell and produces a more ‘orange’ tone than true melanin; this feature needs counteracting during product development.
Challenge: Formulating with DHA
Formulating with DHA is not easy – it has multiple incompatibilities that must be accommodated. For example:
- Formulations must be created with a pH between four and six, but an alkali must never be used during development as it can degrade the DHA. This means all formulations created with DHA need to land within this range or use only acid for adjustments. The pH of a product containing DHA will also typically drop during its shelf life – as low as pH three – so all of the ingredients must be able to tolerate this sort of pH change and range.
- DHA must be transported and stored in refrigerated conditions until the time of use in the formulation and can only be added to a cooled product (less than 38°C).
- DHA is not compatible with ionic emulsifiers and many types of thickeners such as carbomers, sodium carboxymethylcellulose and magnesium aluminium silicate.
- Formulations should avoid the use of oxygen and nitrogen containing compounds, collagen, urea derivatives, amino acids and proteins. DHA works by reacting with amines in the skin, so if it reacts with amino acids and proteins within the formulation, it will reduce the amount of DHA that will react to the skin, reducing its efficacy.
- Iron oxides cause DHA degradation and therefore can’t be used in a formulation for ‘instant’ colouration. Zinc oxide and titanium dioxide also degrade DHA, making them unsuitable to include in self-tanning products with UV protection.
- DHA is a skin-drying ingredient – you need to incorporate suitable emollients and humectants into your formulation to counter that effect so the consumer doesn’t end up with coloured, ‘scaly’ dry skin.
- Colouration will take between 8-24 hours to fully develop and last up to five to seven days.
The tanning agent erythrulose
Another popular tanning agent is erythrulose. This material reacts with free primary or secondary amino groups to form melanoidin too, but creates a more natural looking tan and is less likely to leave streaks, like the orange tint of DHA. However, it can make formulations feel ‘sticky’, so its use is limited to produce more of a golden glow than the depth of colour that DHA can create. While it is less drying than DHA and has less incompatibilities overall, the use of amino acids and proteins must still be avoided, it needs to be refrigerated when stored and added to formulations when cooled (less than 40°C). Erythrulose takes up to two days to develop full colour that then lasts for seven to nine days.
Dark? Fast? Brown? Last?
Want it dark?
If you want a darker result, you can use more DHA but results maximise out at 12-14 percent input. Using more than that won’t give a darker result, but will be drying to the skin, not to mention the strong and undesirable smell! So how can you supercharge the colour? The use of suitable FD&C1 and D&C2 colourants can be used to ‘stain’ the skin while the true colour develops over time, see fig. 2. Used in sufficient quantities, these colourants can stain the outermost keratinocytes the desired ‘brown’ colour until these dead skin cells flake off, so this temporary colour lasts for up to three days.
The products using these colourants are termed ‘bronzers’ by salons and consumers. Not only do these colourants provide an instant colour stain, they can also impact:
- The depth of colour that develops within the first two to three days – so results look darker from the same input of DHA.
- The ‘brown’ of the tan, by overlaying the undesired ‘orange’ tones that can develop with DHA:
- The use of purple tones can be used to make a tan appear a mahogany brown; be wary that too much purple can leave the user looking a bit red or sunburnt.
- The use of slightly green tones can be used to make a tan appear more olive brown, but in moderation so the user does not end up looking like Shrek.
Want it fast?
Using troxerutin in combination with DHA, a faster, more natural brown colour can be achieved. DHA Rapid, by Merck, is used as a tanning accelerator with antioxidant benefits. It has been clinically proven to yield an Individual Typologic Angle (ITA) difference of 2.4 units. In other words, it has shown an increase in skin colour results within as little as four hours after application of 50 percent less DHA, see fig. 3*.
Want it to last?
Using a fast spreading penetration enhancer, like dimethyl isosorbide or ethoxydiglycol, can help ensure even distribution of DHA as well as deeper epidermal penetration. When DHA can penetrate further, less product can yield the same great colour results as well as ensuring a more even spread on application as well as on breakdown. Fig. 4* shows results from using ethoxydiglycol (Transcutol CG by Gattefossé).
Want it brown?
Getting a more natural ‘brown’ than the standard orange-brown of DHA without using colourants can be challenging, but can be overcome by adding melanin to the DHA. Not only does this combination help achieve a more natural-looking ‘brown’, but it also increases the tan intensity – giving a noticeably deeper tan when used regularly. Vegetan Premium by Soliance uses this solution. When tested, over 80 percent of panellists agreed the brown from this active ingredient was more natural looking than using a DHA and erythrulose combination, see fig. 5 and 6*.
Want it real?
Using natural, sustainable micro-algae to stimulate the body’s natural tanning mechanism, a ‘real’ authentic-looking tan can now be developed without the sun. While it won’t give the intense overnight staining effect offered by DHA, Isochrysis Galbana Extract (SymBronze by Symrise) will induce a natural tan in the skin, which accelerates and boosts the skin’s normal response to UV light. The result is a greater tan from less sun – plus it helps prolong a UV-induced tan. A real tan with less UV exposure thus means less skin damage with a great authentic look, see fig. 7.
How to get the best results?
The ‘best’ results will depend on what the concept developer is looking for – is it:
- a longer lasting tan? Remember, this means staining skin cells, so the longevity of the tan relies on holding those cells to the surface of the skin, best achieved through moisturising. Using emollients and humectants will hold moisture in the skin for longer and avoid the appearance of ‘crocodile’ scales.
- a deeper looking tan? Use one of the specialty actives mentioned in this article and/or colourants to increase the colour result rather than just boosting DHA input.
- a faster tan result? Then one of the specialty actives mentioned here should be used, but also colourants can provide instant visible results.
- a more natural looking colour? Again, the specialty actives and colorant agents can help with this
When combining these actives and formulating technologies, it is easy to obtain desired tanning results from your sunless tanning development. Happy tanning!
Author:
Belinda Carli, Director of the Institute of Personal Care Science (IPCS)
belinda@personalcarescience.com.au
www.personalcarescience.com.au