Women who use make-up on a daily basis are absorbing almost 5lb of chemicals a year into their bodies, it is claimed.
Out-of-date lipstick may be a hothouse for bacteria.
Many use more than 20 different beauty products a day striving to look their best while nine out of 10 apply make-up which is past its use by date.
Dependence on cosmetics and toiletries means that a cocktail of 4lb 6oz of chemicals a year is absorbed into the body through the skin.
Some synthetic compounds involved have been linked to side effects ranging from skin irritation to premature ageing and cancer.
Richard Bence, a biochemist who has spent three years researching conventional products, said: "We really need to start questioning the products we are putting on our skin and not just assume that the chemicals in them are safe."We have no idea what these chemicals do when they are mixed together, the effect could be much greater than the sum of the individual parts."
Mr Bence, an advocate of organic beauty products, believes that absorbing chemicals through the skin in more dangerous than swallowing them.He said: "If lipstick gets into your mouth it is broken down by the enzymes in saliva and in the stomach. But chemicals get straight into your bloodstream, there is no protection."
Warnings over using out-of-date lipstick and mascara have also been issued by the Royal College of Optometrists which believes such items are a "hothouse" for harmful bacteria.
Clio Turton, of the Soil Association, said: "Many women are using over 20 different products a day, bombarding themselves with hundreds of different chemicals. They should be asking themselves 'is that eyelash conditioner really essential?'
Among chemicals under scrutiny are parabens (para-hydroxybenzoic acids) which are preservatives used in products including soap, shampoo, deodorant and baby lotion. Traces of parabens have been found in breast tumour samples, although its link to the development of the cancer is disputed.
Sodium lauryl sulphate, used to help create lather in soaps, shampoo, shaving foam, toothpaste and bubble bath, can cause skin irritation.
The Cosmetic, Toiletry and Perfumery Association said there was no reason for worry because the products were covered by European Union rules requiring them to be safe.
A spokesman said: "The cocktail effect is an urban myth. We do know how different chemicals react individually and can predict how they interact with each other and this is taken into account when the safety of products is assessed."
