Suffering with a headache or runny nose in the office doesn't always mean you've been staring at the computer too long, or are getting a cold.
It may be the actual work environment that's making you ill.
The charity Allergy UK estimates that around 5.7 million people in the UK could be allergic to their workplace, after its research found that 95% of office workers questioned suffered from a multitude of health problems caused by their office environment.
Nearly all of the workers, who were primarily allergy sufferers, had one or more symptoms including headaches, nasal problems, eye conditions, dry throats, breathing difficulties, lethargy and skin irritations in the office.
More than a quarter (27%) said their symptoms got worse in the office, with 62% having experienced itchy or watery eyes, and 27% having had breathing difficulties in their office over the last year.
Allergy UK suggests such symptoms may be caused by allergic reactions to dust and plant spores in the office, and even pet allergens brought in on colleagues' clothes.
Fortunately, allergic employees don't need to change jobs to improve their health - just opening windows, regularly wet-dusting surfaces and making sure carpets are well-vacuumed are some of the simple measures that can reduce indoor allergies.
Lindsey McManus, deputy chief executive of Allergy UK, points out that many people who are allergic to their offices may not have made the connection between their symptoms and the workplace.
She says: "People who get thick heads, blocked-up noses and sore eyes that they just put up with ought to think about whether it's caused by something at work.
"You might have had a week off and felt fine and then gone back to work and got the symptoms again. Ask yourself what it could be.
"It might not be severe enough to stop you working, but it could be addressed relatively easily - simple changes can really make a difference."
There are numerous 'hotspots' around the office that can have huge implications for allergy sufferers, particularly closed windows, carpets, bookcases and plants.
A key problem is lack of ventilation, and the majority of people with allergy symptoms at work don't think their office has enough circulating air - of those questioned, only 15% said their office was well-ventilated.
Most office workers reported that their workplace had carpeted floors, but carpets and soft furnishings can harbour house dust mites - a major cause of allergies.
More than a third of offices contain plants, and they can harbour moulds which release spores that can cause allergic reactions.
Even colleagues can be responsible for triggering allergies in their workmates, because of the pets they keep at home. The Allergy UK survey found that 34% of respondents had a pet allergy, and might therefore react to allergens (pet dander) brought in on other people's clothes, especially cat hairs. For the 61% of those questioned who sat within a metre of someone else, this risk was even greater.
The study also showed that cleaning of offices is infrequent and doesn't appear adequate enough to prevent the build-up of house dust mites and allergens, with 37% of respondents saying their office was cleaned just once a week or less.