Contrary to popular belief, stripes that run across the body are more slimming than supposedly flattering vertical stripes, according to the research by Peter Thompson of the University of York.
The study was based on the Helmholtz square illusion, created by 19th century scientist Hermann von Helmholtz who drew two identically sized squares and put vertical stripes on one and horizontal stripes on the other.
That experiment showed the square with the horizontal stripes appeared taller and thinner than the other square, prompting Helmholtz to recommend ladies wore horizontal stripes to make them look taller.
To reach his conclusion, the expert asked people to compare more than 200 pairs of pictures of women wearing horizontally and vertically striped dresses.
He then asked them to say, in each case, which of the two they thought was fatter.
His experiment revealed that when the two women were the same size, the one wearing the horizontal-striped dress appeared to people to be the thinner of the two.
And to make the women appear to be the same size, the one wearing the horizontal stripes had to be six per cent wider.
"We carried out a number of experiments both with squares and oblongs and pictures of women wearing horizontal and vertical stripes," Telegraph quoted Dr Thompson, as saying.
"Horizontal stripes don't make you look fat. The one wearing the vertical stripes looks wider than the one wearing the horizontal stripes.
"Horizontal stripes, if anything, make you look thinner," he added.
Dr Thompson said it was not clear why the visual illusion existed, although it could be that the horizontal stripes made an image more 3D and introducing depth could reduce width.