Cosmetics have been in use since time immemorial. In earlier ages several potentially toxic inorganic pigments such as malachite, mercuric sulphide or white lead were used in cosmetic preparations. In contemporary products several organic components such as parabens, alkylphenols, etc have also been included. It was a common concept that cosmetic products were only meant for external applications and therefore were safe as skin was believed to be impermeable to external applications. However, it is now established that skin is not an impermeable barrier which can prevent penetration of chemical compounds present in cosmetics. A common user is primarily concerned with irritations and allergies only due to use of such products but it has been established that systematic absorption can cause chronic toxicity resulting in harmful consequences.
It is also a common belief that cosmetic products are safe as the cosmetics industry is under regulation of US Food and Drug Administration. On the contrary this is a self regulated industry. Undoubtedly there are several established global brands which exercise strict quality control during manufacturing but it is also true that in the grey markets, especially in third world countries, counterfeit products find a flourishing market. Such fake products are not manufactured under any controls worth mentioning and their use can do more harm than good.
Cosmetics come in various forms such as lipsticks, soaps, toothpastes, body deodorants, face powders, nail polishes, shaving creams, face creams and anti- ageing creams, sunshades, moisturizers, shampoos, hair oils, etc. The list is virtually endless and new products are continuously being added to keep pace with growing consumer demands. The formulations are available as powders, creams, gels, lotions and liquid suspensions containing un- dissolved solids. Several techniques find use in analysis of cosmetic products some of which are Transmission Electron Microscopy, Atomic Force Microscopy, X-Ray Fluorescence, Laser Desorption Ionization Mass Spectroscopy, Inductively Coupled Optical Emission Spectroscopy and X Ray Diffraction analysis. Most of the mentioned techniques involve high initial investments so become unaffordable by common testing laboratories. Out of these XRD is affordable and does provide valuable information on components which exhibit crystalline or semi-crystalline properties. However, the role of expensive instruments cannot be underplayed and should be restored to when specific details on sample constituents are required.
X-ray diffraction reveals the proportion of crystalline and amorphous content of a product. Sharp peaks result from the crystalline content and amorphous content results in broad humps. The identity of crystalline compound and can be established through a match with the data base of known crystalline materials.
XRD is a non- destructive technique which also does not require sample pretreatment or dilutions. It makes use of a collimated beam of x-rays that is directed onto the sample holder,tube or a powder smeared evenly on a glass slide. The diffraction pattern results from constructive interference of beams scattered by the faces of crystal planes of the sample. The x-ray incident beam scans the sample over a range of degrees by rotating the sample stage at a predetermined angular scan rate
Nanotechnology has brought about a revolution in fields of materials science, electronics, pharmaceuticals, foods, etc. Cosmetics have not been left out and nano particles (having diameters below 100nm) are being increasingly used to improve the desirable features of cosmetic products. Nano emulsion in the form of lotions and conditioners are commonly available. Studies are reported on nano emulsions used in sunscreens comprising of TiO2 nano particles. Similarly silver nano particles find use in some soaps, toothpastes and face creams and act as bactericides. Similarly other nano particles have shown promise in other commonly used cosmetic products.
X-ray diffraction has played a significant role in studies on such particles as their properties achieve the desirable cosmetic features and also their uptake by the skin.