The categories of preservatives used in the cosmetics are various. Those that now I write are substances that yield (free) formaldehyde, one substance with a toxicological level much high, quite classified officially (not by me) like cancerogenous.
However this thing would not have to alarm to us too much because the law places a strict quantitative limit for the employment of these substances (comprised between 0.1% and 0.6%) beneath the potential risk threshold (theoretical).
These substances can however cause to irritations and negative effects on the skins.. SO PAY ATTENTION please
5-BROMO-5NITRO-1.3-DIOXANE (it is most powerful, personally i avoids it always. Also the companies is discarding it nearly of all)
2-BROMO-2NITROPROPANE-1.3DIOL (it is like first but less powerful, it's better to avoid ALWAYS if it is in a product for frequent use)
DMDM HYDANTOYN (little better of previous)
DIAZOLIDINYL UREA (lighter than hydantoin)
IMIDAZOLIDINYL UREA (like previous but the less powerful)
COCAMIDE (DEA-MEA-MIPA) often appears on labels as Cocamide DEA and are commonly found in cleansers, shampoos and body washes as an emulsifier and foaming agent. According to a 1998 research study by the National Toxicology Program, these chemicals affect hormone function and are known to produce cancer causing nitrates and nitrosamines in laboratory animals. The FDA is currently evaluating the link between DEA and cancer in humans.
COCAMIDE, in combination with some surfactants (SLES and by-products ), strengthens negative effects at aesthetic level (the solution gets more aggressive) and at tossicologic level (they free Nitrosamine)
SODIUM CHLORIDE it is used to thicken the emulsions. It is used with great facility for its reduced cost. Toxicologically it is innocuous, but to aesthetic level, if used (like unfortunately often it is employed) in high amount cracks the keratin of the hairs . (All we know the effect of the baths in sea on the hairs, the effect of the saltiness)