Women look their oldest at 3.30pm every Wednesday because it's the day when energy levels plummet, work stress is at a peak and the effects of any weekend late nights finally kick in, according to a new study. The research, carried out by the tanning brand, St Tropez, revealed that one in ten women find Wednesday the most stressful day in a typical week. Two thirds experience a "slump in energy levels" mid-afternoon every Wednesday, the Telegraph reported. This forces a quarter of women to reach for a sugary snack on a bid to boost their mood and energy. But the next day, Thursday, is the day they are most likely to have sex, according to the study. Sex gives them a youthful rosy glow, which could explain why women feel so happy on a Friday - the day named as the happiest day by 60 per cent of women. Another reason why women look their eldest mid-week could be a boozy treat at the weekend. Nichola Joss, St. Tropez skin expert explained that it can take up to 72 hours for the visible effects of alcohol to show, so the effects of drinking on the weekend may not present themselves until Wednesday afternoon. The shock of going back to work leaves 37 per cent of women sleepless on Monday night - another reason for the mid-week slump. The effects of a lack of sleep can take 48 hours to show on the face, so if many women sleep badly on Monday they will look their oldest on Wednesday, Joss said. Further more than one in ten women will abandon their skin care regime on a Wednesday. It's essential to cleanse the face of build up from everyday pollution. Letting these build up clogs the skin making it duller and drier, and superficially older, Joss added. ANI