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Photosensitivity is an abnormal sensitvity to ulturviolet (UV) radation, or sunlight. It can be the result of a genetic predisposition, whereby the body cannot repair skin damage caused by exposure to sunlight or certain chemicals. The primary types are phototoxicty and photoallergy.

Phototoxicity {a non-immunologic reaction) occurs skin exposed to sunlight or other UV radiation becomes damaged as a result of photoactive chemicals (chemicals that are able to absorb UV radiation) entering the the viable (living) elements of skin and and reacting under UV lightto bring about cellular damage.

The main symptom of phototoxicity is sunburn, which can lead to severe blistering. Acute photoxic reactions include erythema (skin redness produced by capillary congestion), oedema (swelling caused by by fluid in the body tissues), leading to hyperpigmentation (where patches of skin grow darker in colour then the surrounding skin), and even skin cancer.

The FDA have reported the discovery of potentially phottoxic agents in deodorants, antibacterial soaps, artificial sweetners, cadium sulphide (chemical injected into the skin during tatooing) and fluoroscent brightening agents for cellulose, nylon and wollen fibres, mothballs and petroleum products.

PHOTOALLERGY (an immunologic reaction) occurs on re-exposure to a chemical to which the individual has previously become sensitized. It is often characterized by an intense, eczema-like skin rash on exposure to sunlight. In a photoallergic reaction substances either made by the body or from outside are transformed by UV radation into antigens (substances that prompt your immune system to generate antibodies against them).

Symptoms can appear within 20 seconds of being exposed to sunlight, although they may also be delayed.

The once commonly used sunscreen ingredient para-aminobenzonic acid (PABA) is known to cause photoallergic reactions, as are cinnamates,avobenzone, oxybenzone, padimate O, benzoylmethanes, musk ambrette and sandalwood oil. In fact, there are numerous cosmetic ingredientsthat have now been shown to cause phototoxicty.

Research published in the scientific journal Food and Clinical Toxicology found that under sunlight six lipsticks and five facial creams generated reactive oxygen species (products of normal metabolism that can damage cell structures if levels become too high in the body, triggered haemolysis (the breakdown of red blood cells) and caused lipid peroxidation (cell damage caused by free radicals stealing electrons from fats in cell membranes).

It is thought that lipid peroxidation may play a vital role in certain aspects of the ageing process.

Given the many ingredients used in cosmetics are marketed as anti-ageing miracles, it seems some what ironic that some of them can break down into toxic chemicals under UV light. Retinyl palmitate, a vitamin A derivative touted as an anti-ageing ingredient, decomposed under UVA light into chemicals that have been shown to be photomutagenic in mouse lymphoma cells.

Other vitamin A dervatives can also cause phototoxic reactions.

The research authors concluded that repeated use of products containing phototoxic agents may lead to skin ageing, along with other problems such as erythema, oedema and photomutation (UV) radiation-induced damage to DNA or sequence of a gene). Bronopol (2-bromo-2-nitropropane-1,3-diol), used as a preservative and antiseptic in cosmetics, toiletries and topical medications, has been shown to be phototoxic in vitro, depending on the UV doses administered and concentration of the compound.

This suggests that it could potentially cause photosensitization when applied dermally.

Certain sun tan accelerators and perfumes contain bergapten (or 5- methoxypsoralen0, a phottoxic component of bergamot oil that can cause berloque dermatitis, a skin condition characterized by discolouration of the skin.

According to one study, bergapten accounts for aroun 67% of the absorption of UVA and UVB light by bergamot oil.

Alpha hydroxy acids (AHAs), also commonly referred to as fruit acids, such as glycolic acids, malic acid, lactic acid and salicylic acid, have been lauded for their alleged 'anti-ageing' activity, because of their ability to remove the outer layer of skin revealing a 'younger looking you'. But they can also cause photosensitivity. In one study AHA glycolic acid elevated the sensitivity of human skin to sunburn by as much as 50 per cent in some individuals.

Other topically applied substances with photoxic potential include certain dyes (such as anthraquinone, Disperse Blue 35 and cosin dyes), fragrances, plant products (such as figs, limes, parsnips, fennel and dill and coal tar components (such as acridine, anthracene, phenan threne and pyridine).

Certain pharmaceutical preparations such as particular antidepressants, antihistamines, anitbiotics, antipsychotics, antiparasitics, diuretics, hypoglycaemics, non- steroidal anti-inflammatory drugs (NSAIDS), chemotherapy drugs and oral contraceptives can also cause photosesitivity. Various essential oils, such as bergamot and sandalwood (as mentioned above, citron, lavender and cedar can cause photosensitivity, as can the herb St.John's wort.

Did you know?

Our staid styling friend, hairspray, pretty much glues our whispy strands together with 'liquid plastic' and perhaps worse. When you push that little button on an aerosol hairspray beads of polymer drip onto your hair shafts and bind them together, keeping your hair in a fixed position.

Some individuals, having experienced repeat exposures to hairspray, suffer from symptoms such as acute upper respiratory infections, shortness of breath, frequent colds, chronic cough, and in certain instances, X-ray abnormalities.

Reference: Toxic Beauty: Dawn Mellowship

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