CAFFEINE is a quite common cosmetic ingredient. It can be found mostly in eye creams or anti-cellulite products but lately it has been added even to soaps or shower gels.
Chemical Name: Caffeine
Chemical Formula: C8-H10-N4-O2
Molecular Weight: 194.2 g/mole
pH (1% soln/water): 6.9 [Neutral.]
Solubility: The product is equally soluble in oil and water; log(oil/water) = -0.1.
Caffeine is moderately soluble in water at room temperature (2 g/100 mL), but very soluble in boiling water (66 g/100 mL). It is also moderately soluble in ethanol (1.5 g/100 mL). It is weakly basic (pKa = ~0.6) requiring strong acid to protonate it.
Incompatibilities with Other Materials: Strong oxidizing agents.
Hazardous Decomposition Products: Nitrogen oxides, carbon monoxide, irritating and toxic fumes and gases, carbon dioxide.
(Source: here and here)
Caffeine has been demonstrated to have anti-inflamatory and antioxidant activities. In vitro it was proven to stimulate the lipolysis in metabolism studies on fat cells, but what can be seen in vitro doesn’t necessarily mean that it is going to work the same way in a topic application.
A study also showed that topical application of caffeine reduces the risk of photo-induced cancer in mice.
(> Koo SW, Hirakawa S, Fujii S et al. Protection from photodamage by topical application of caffeine after ultraviolet irradiation. Br J Dermatol. 2007 May;156(5):957-64. Epub 2007 Mar 28.)
Caffeine is supposed to have these properties (as I said above, there are no studies at the moment that prove these properties can be achieved with a topical application, but this doesn’t mean that such properties don’t exist all together):
- Vasocostrictor – it affects the muscles of vessels (specially the small ones) and as a consequence it should reduce redness of the skin (in particular in cases of rosacea) and it should decrease the blue circles around the eyes (caused by “leaking” vessels)
- Antioxidant – it is good to formulate trying to create a synergy with other antioxidant to inhance this property
- Anti-cellulite – this comes as a conclusion about the in-vitro studies on the metabolism of fat cells.
Solubility/how to use it in formulations: Caffeine is soluble in very small amount in water but it is largely soluble in heated water, so it is one of those few Active Ingredients which you should add in the Phase A.
Percentage of use: it is generally added from 0.5% to 3%. In the eye area it shouldn’t be added more than 1.5%. Usually in creams I like to add 2%, but to some people with particularly sensitive eye area it is better to use 1-1.5% only (if you think your eyes are very sensitive, try making this cream with 1% only… if you have no bad reaction next time you can try increasing it to 1.5% 🙂 ).
Problems in formulation: it is soluble in hot water but once the water cools down it tends to crystalyze forming typical “needles”. These “needles” are actually soft and disappear if you apply the product anyway but this is not something I suggest you to do. The way to avoid this from happening is:
– keep stirring until cool down (you should do this for every cream even if it doesn’t contain caffeine, but in case you added caffeine you just have one more reason to do so 🙂 )
– don’t add too much caffeine (I wouldn’t exceed the 2% guideline).
Now to my personal comment:
I do like caffeine: it is a cheap and, in my opinion, effective ingredient.
I do like it in the eye area (I tend to have blue circles and sometimes puffy eyes) and I have seen “the difference” if I applied creams that didn’t contain it.