It’s one of fashion’s biggest faux pas.

Wearing white after Labour Day might spur the wrath of your mother or grandmother but where exactly did the rule come from? It turns out the explanation is most likely practical.

Dating back to 1872 in Canada and 1894 in the United States and falling on the first Monday in September, Labour Day has over time become the unofficial end of summer.

WATCH: How to keep white in your wardrobe after Labour Day

In a strictly practical sense, wearing lighter white clothing reflects less heat from the sun, making the clothing cooler in on hot sunny days. As seasons shifted, it only made sense to switch up your clothes for more appropriate attire.

But why if the temperature remained hot into September? And why did it become a sign of fashion etiquette to ditch your white summer dresses and white linen suits? Like many staples of fashion etiquette, the reason could also be class-based.

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In the first half of the 1900s many of society’s elite spent their summer months at summer homes lounging seaside or by a lake. This break from urban life, like most events, required a completely different wardrobe, one that included lighter attire with white, bright colours.

READ MORE: How to wear white after Labour Day (yes, it’s OK)

When suitcases were packed back up and the well-to-do returned to the ‘real world’ those clothes were stashed in the back of the closet. Labour Day, signaling the end of fun-in-the-sun for those that could afford it, was the defacto cut-off day for the summer wardrobe.

But does the old adage still apply?

According to fashion bibles Vogue and Chatelaine, both say to throw the rule out the window. Wear what you like, but choose material that coincides with the weather. If you’re comfortable and confident, chances are no one will take a second look.