With Christmas just over a month away, customers may have already noticed festive songs ringing in their ears as they shop. Retailers claim the catchy, instantly familiar tunes put shoppers in a positive mood.

The tradition, which sometimes begins as early as October, infuriates many, especially those who think it is far too early to get into the festive spirit.

Now one expert has given shoppers a valid excuse for feeling like Christmas grumps. Psychologist Linda Blair claims repetitive songs can be damaging to mental health.

"Christmas music is likely to irritate people if it's played too loudly and too early, she said to Sky News.

Employees who are required to listen to the same songs dozens of times a day are particularly affected. She says many struggle to "tune it out" and they become "unable to focus on anything else."

"You're simply spending all of your energy trying not to hear what you're hearing."

"It might make us feel that we're trapped – it's a reminder that we have to buy presents, cater for people, organise celebrations. Some people will react to that by making impulse purchases, which the retailer likes. Others might just walk out of the shop. It's a risk."

Another song UK viewers will be hearing over and again for the next two months is the John Lewis Christmas advertisement soundtrack. The annual campaign, usually launched in early November, marks the start of the Christmas run-up for many people.

A mysterious video trailer with the hashtag #UnderTheBed was released on Twitter yesterday, prompting speculation that the new advertisement will feature a large huggable monster playing the central role.

Shoppers queue outside Selfridges on London\'s Oxford Street.
Frah-steee the snow-mannnnn Reuters