Vertical stripes don't flatter – they make you look fatter

Women of a certain age will be replacing their wardrobes and Geordie football fans will be crying into their Newcastle Brown Ale. Scientists have discovered that the fashion mantra that wearing vertical stripes makes you look thinner is not true. In fact, horizontal stripes are more flattering to those with a less than perfect physique.

The accepted wisdom from fashion gurus is that an outfit with vertical stripes appears to elongate your figure by drawing the eye up and down. Horizontal stripes supposedly do the opposite, making that unruly paunch look even larger than it actually is.

But when Dr Peter Thompson, a psychologist and expert in visual perception at the University of York, tested the optical illusion he found the opposite was true. "Horizontal stripes don't make you look fatter," he said.

His test involved showing pairs of pictures of women to volunteers. In each pair, one woman was wearing a dress with vertical stripes and the other was wearing horizontal stripes. In each pair the vertically striped figure was the same woman, but the horizontally striped figure was either slightly fatter or thinner. The subjects had to choose which they thought looked more rotund.

By analysing the choices made by around 20 subjects he found that the vertically striped figure had to be 6% slimmer for them to judge the two women to be the same size. When both images in the pair were of identically sized women, people tended to judge the horizontally striped woman to be slimmer – contrary to received wisdom.

Thompson, who presented his work at the British Association Festival of Science, said the effect is a version of the Helmholtz illusion, an optical effect in which a square with horizontal stripes appears taller and thinner compared with an identically sized one with vertical stripes.

The man who discovered the illusion, the 19th century German physicist and physician Hermann von Helmholtz, gave out different fashion tips. "Helmholtz actually said that women wear horizontal stripes to make themselves look taller so in the 19th century wearing horizontal stripes had a completely different belief attached to it than it does now," said Thompson.

Another fashion tip for those who want to appear more lithe appears to be reliable, though. According to Thompson, wearing a black dress is a good strategy for hiding those excess pounds because of a separate optical illusion.

"Wearing black is a good thing," he said, "That one works because we know that a black circle on a white background looks smaller than a white circle on a black background."

However, Thompson's study of optical illusions casts doubt on another piece of popular wisdom. He believes that the standard advice from estate agents to show off your house with clear, uncluttered rooms is wrong. Filling up rooms with furniture should make them appear slightly bigger than they actually are, he said. Patterned wallpaper has the same effect.

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