Evidence of oxidative stress can appear under other conditions, including exposure to certain environmental pollutants or infections in the urinary genital tract.

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It may be provoked by infection with Chlamydia trachomatis, a sexually transmitted denizen of the genital tract, and Ureaplasma urealyticum and Mycoplasma fermentans, two other inhabitants of the genitals.

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Mr Dilly Anumba, a consultant obstetrician at Sheffield University who has recently published work showing that TLRs are present in the female genital tract, said Professor Bennett's theories were logical and well worth pursuing.

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It enters the body through tiny breaks in the skin caused by rubbing during sex, making its way below the surface to worm inside immature skin cells in and around the genital tract, (see diagram, below).

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