Workers sitting next to windows are in danger of developing skin cancer down one side of their face, an expert has warned.
Harmful ultra-violet rays can travel through glass, leading dermatologist Dr Rosemary Coleman said.
She said sunblock should be worn indoors all year round to protect from the rays, which also penetrate car windows, leaving those who drive a lot also at risk.
The Blackrock Clinic expert said people should not underestimate the strength of the Irish sun and wear factor 50 in an effort to decrease rates of skin cancer in the country - the 14th highest in the world.
"It's the office workers who go out for a blast of sun at lunchtime when the UVA index is at its highest that are the people getting more skin cancers than those who work outside," she said.
"I find few of my patients seem to know that UVA rays travel through glass, through cloud and through car windows.
"I have observed a number of people who come in to me with severe sun damage down one side only and I discover they're drivers or indoor workers such as primary school teachers.
"It's these teachers that often sit at the same desk in the same classroom for years and years with the sun coming in on one side of them."
Secondary teachers moved around more to different classrooms, she added.
People who drive for a living should also be mindful of the sun coming through the vehicle's windows," said Dr Coleman.
"Depending on the make and model of car, the windscreen will protect you from UVA rays up to 90pc, but the side windows will only protect you about 40pc.
"I always recommend people should keep sunblock in the car at all times, and people who drive a lot should wear sun gloves that protect hands from ageing."
Dr Coleman also warned that the strength of the Irish sun should not be underestimated.
"The Irish have a very high tendency to think our sun is weaker because we get less of it. In fact, the Irish sun has a very high UV index," she said.
"Ireland has the 14th highest rate of skin cancer in the world, which is amazing when you consider New Zealand is top, followed by Australia.
"We have bad sun practices here. My philosophy is to look at sunscreen as the best anti- ageing moisturiser you can get and wear it 365 days a year, regardless of weather. Get into the habit of automatically putting it on each morning.
"Use factor 50, as studies show the average person puts on so little they're only actually getting a factor of 19.27.
"You have to put almost a full teaspoon on your face to get factor 50 strength, and most people don't do that. So put factor 50 on and re-apply every two hours if you're outside."
Skin cancer is the most common cancer in Ireland.