Almost one-and-a-half million Australians work on shifts; a job situation that has been linked to health and safety problems as well as reduced performance. In the U.S., over 22 million workers are on evening, rotating or on-call shifts.

If you’ve travelled by plane for more than a few hours, you’re probably one of the more than 90% of all air travellers who have suffered the effects of jet lag. Business travellers find they underperform for the first day or two after travel. Vacationers complain they don’t feel up to enjoying the sights for at least a day while their bodies recover.

Biology and lifestyle have a big impact on how much women sleep, and it is further impacted by women not giving sleep a high enough priority. People don't understand that "sleep is a biological need," says Dr Jeffrey Barasch, director of The Valley Hospital Sleep Centre in Ridgewood, New Jersey.

Sleep masks are used at home, in a hotel, or while travelling as a passenger in a car, train, or airplane to block out either natural light (sunlight) or artificial light. Night shifters use them to sleep during the day and patients in hospitals use them to block out light emitting from the hallway. Others use them simply to relax or meditate or block the light when their partner is reading in bed.