At least 12 million Britons could be allergic to their own homes, according to a new survey.
Allergy UK said "home fever", also known as perennial allergic rhinitis, is on the rise, with more sufferers seeking help for symptoms including a runny nose and sneezing.
A poll of 1,600 people with allergies found 58% react to house dust mites, 31% said they were allergic to mould and 45% had a pet allergy.
Some 30% of sufferers are also allergic to the chemicals found in common cleaning products.
NHS figures suggest 12 million people receive allergy treatment in any one year and six million are so seriously affected they require specialist help.
Hospital admissions for allergy have risen over the last two decades.
Some estimates suggest 21 million people in the UK now have some sort of allergy.
Today's poll for Allergy UK found 59% of indoor allergy sufferers said their symptoms are worse in the bedroom.
Estimates suggest a bed can house two million house dust mites while the average pillow doubles in weight over a period of six months due to dust mite faeces.
While there is no cure for home allergies, the charity recommends people take simple steps to cut the number of allergens in their home.
These include dusting regularly with a damp duster followed by a dry cloth, washing bedding once a week at 60 degrees or higher and regularly steam-cleaning carpets and curtains.
Other tips include using allergy protectors on mattresses, duvets and pillows, replacing the mattress every eight to 10 years and buying new pillows every year.
Allergy UK research suggests 16% of people wash bed sheets every three weeks or less while 58% wash bed linens between 30 or 40 degrees, which is not high enough to kill mites.
It also found 13% of people have had their current mattress for 11 years or more while 25% keep pillows for five years or more.
Lindsey McManus, from Allergy UK, said: "Indoor allergies are on the increase.
"In February 2010, house dust mites were a trigger of an allergic reaction for 45% of allergy sufferers.
"Fast forward 18 months and that figure has risen to 58%.
"In the winter months, we see calls to the Allergy UK helpline peak as more and more sufferers come forward.
"In an effort to keep warm, people close doors and windows, turn up the heating and inadvertently create the ideal breeding ground for house dust mites.
"The home is somewhere we escape to but for millions it is the trigger of an allergy.
"Confusion frequently arises during colder months as people develop cold and flu symptoms and treat them as just that.
"Runny nose and sneezing are in fact the most common indicators of a house dust mite allergy, so the nation is not treating the root cause of the problem, just the symptoms."
Indoor Allergy Week runs from November 14 to 20.