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The word placebo, Latin for “I shall please”, dates back to a Latin translation of the Bible by Jerome. It was first used in a medicinal context in the 18th century. In 1785 it was defined as a “commonplace method or medicine” and in 1811 it was defined as “any medicine adapted more to please than to benefit the patient”, sometimes with a derogatory implication but not with the implication of no effect. Placebos were widespread in medicine until the 20th century, and they were sometimes endorsed as necessary deceptions. In 1903 Richard Cabot said that he was brought up to use placebos, but he ultimately concluded by saying that “I have not yet found any case in which a lie does not do more harm than good”. In 1961 Henry K. Beecher found that patients of surgeons he categorized as enthusiasts relieved their patients' chest pain and heart problems more than skeptic surgeons. In 1961 Walter Kennedy introduced the word nocebo.

Mechanism of the effect

The phenomenon of an inert substance resulting in a patient's medical improvement is called the placebo effect. The phenomenon is related to the perception and expectation which the patient has; if the substance is viewed as helpful, it can heal, but if it is viewed as harmful, it can cause negative effects, which is known as the nocebo effect. The basic mechanisms of placebo effects have been investigated since 1978, when it was found that the opioid antagonist naloxone could block placebo painkillers, suggesting that endogenous opioids are involved.

Some unintended effects of chemicals found in cosmetics

Unfortunately, sometimes the ingredients in cosmetics can have unintended side-effects. For example, skin allergies (allergic dermatitis) to specific ingredients can be a problem. Allergies to cosmetic products can be due to chemicals such as added fragrances and preservatives. This can lead to a skin rash where the product is applied. If you think you may be allergic to a cosmetic product, it is important to determine which ingredients may be causing the problem. A specialised allergy test, called a patch test, may be helpful in this. Chemicals causing the allergy can then be avoided by reading product labels. Other people, while not allergic to a specific ingredient, may nevertheless find that a product irritates their skin because it damages the outer layers - a condition known as irritant dermatitis.

Exfoliates and skin peels leave the skin underneath temporarily more vulnerable to sun exposure because they remove the outermost protective layer of dead skin cells. Over-washing of hair or skin with soaps and detergents can strip the skin's natural protective oily layer, resulting in dry and scaly skin. Alternatively, excessive use of make-up or oily moisturisers can block pores and aggravate acne.

More serious side effects have been suggested for certain cosmetic ingredients. For example, a recent study was published that linked breast cancer with deodorants. The focus of the study was on parabens, a class of chemicals commonly used as preservatives in deodorants and antiperspirants. While parabens were found in breast cancer tissue, the study did not establish that they were the source of the cancer nor did it identify underarm cosmetics as the source of the chemicals.

A recent US study found that many cosmetics and toiletries used worldwide contained chemicals that were either known cancer-causing agents (carcinogens) or were untested for their effect on human health. More research into the safety of cosmetic chemicals is needed.



Date: 2015-01-29; view: 1544

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