For most of us, putting up the Christmas tree and the decorations is guaranteed to produce festive cheer.
But ever since Lisa Smith was a teenager, she has dreaded the annual tradition - not because she is a Scrooge, but due to a mysterious illness it brings on.
Every Christmas the festivities have coincided with constant sneezes, streaming eyes, a pounding headache and a nose as red as Rudolph's.
She has just had to put up with it, but this year she has finally discovered the reason - she is allergic to Christmas, particularly the pine in trees.
'From the moment the first Christmas trees went up in the shops, I'd plunge into what felt like a constant flu,' said Miss Smith, a swimming instructor.
'Even on Christmas Day, I'd find it impossible to feel excited about opening presents and would sneeze, cough and blow my nose throughout dinner.'
It was her fiancé Phil French, 27, a City worker, who suggested she may be allergic to Christmas.
'I thought this was a ridiculous idea,' she said.
But after research on the Internet she discovered it really was a condition.
Christmas trees are the trigger with their pine needles and strong-smelling sap, but decorations covered in dust from being stored away all year can also cause problems.
She went to her GP who confirmed the diagnosis.
'She said my symptoms mirrored those of a severe hayfever sufferer. She was certain the main trigger was pine sap,' said Miss Smith, 26, from East London.
She is not alone. According to an American study, one in seven people experience some form of respiratory allergy to Christmas trees.
Dr Mike Smith, a specialist in preventative medicine, said: 'Like all plants, live Christmas trees hide mould, contain sap and release spores into the air, which can trigger allergic reactions.'
Miss Smith now avoids real Christmas trees and uses a seawater nasal spray called Sterimar.
She said: 'This will be the first time in over a decade I'll be able to have a normal Christmas.
'It will be a relief to open my presents and have a Christmas dinner without feeling unwell.'