Women look their oldest at 3.30pm every Wednesday, a study has found, because that is when energy levels plummet, work stress is at a peak and the effects of any weekend late nights finally kick in.
The research shows one in ten women (12 per cent) find Wednesday the most stressful day in a typical week.
But they reveal Thursday is the day they are most likely to have sex.
It gives them a youthful rosy glow which could contribute to why women feel so happy on a Friday – 60 per cent name it as their happiest day.
A quarter of women feel stressed several times a week – while one in five (19 per cent) admit they will work through Wednesday’s lunch hour.
The study, carried out by the tanning brand, St Tropez, revealed two thirds experience a “slump in energy levels” mid-afternoon every Wednesday.
This forces a quarter of women to reach for a sugary snack on a bid to boost their mood and energy.
Nichola Joss, St. Tropez skin expert, said: “It’s fascinating that 3.30pm on a Wednesday is the time women look their oldest.
“Combine the highest stress levels of the week on a Wednesday with the natural mid-afternoon slump and it seems that’s why women can look older than their years.”
And Ms Joss revealed how a woman’s sex life can have a big impact on how they feel.
She added: “Many women credit a healthy sex life for keeping them looking and feeling young.
“As the mid-week slump passes and stress levels begin to decrease, it’s fascinating that Thursday is the evening they are most likely to feel amorous.”
Almost half of women (46 per cent) are likely to indulge in a boozy treat at the weekend – another reason why women look their eldest mid-week.
Ms Joss says it can take a few days for the signs of the boozy weekend to show.
She added: “Processing the toxins in alcohol and sugar can put strain on the body.
“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 was shown to give many women sleepless nights.
More than a third (37 per cent) reported Monday night is when they are most likely to get a bad night’s sleep.
Ms Joss added: “A lack of sleep on a Monday does not bode well for how the skin will look on Wednesday.
“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.”
Further findings showed that the average British woman gets six hours and 43 minutes sleep a night.
Ms Joss continued: “For maximum anti-ageing benefits it’s essential women get 7 to 8 hours sleep a night.
“Too little and your skin cells can’t rejuvenate, too much can result in puffy, older looking skin.”
Another effect of the mid-week slump is that more than one in ten (12 per cent) women will abandon their skin care regime on a Wednesday.
Ms Joss added: “Even if a woman doesn’t wear make-up, 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.”
And 15 per cent of women begin using anti-ageing products between the age of 21 and 25 – which proves to be an important weapon against ageing.
Mary Collins, 31, from Portsmouth, said: “After having a drink on the weekend, the tiredness definitely catches up with me by Wednesday.
“But I’m always hoping I have a special night on Thursday. A bit of romance makes me feel younger and happier – and Friday is when I feel my best.”
The research was carried out to support the launch of St Tropez Gradual Tan Plus Anti-Ageing Face.