A new study has shown that allergy sufferers who experience high levels of stress or anxiety can be substantially more likely to suffer a potentially life-threatening reaction the following day.
The research by scientists in the US suggests that people with hay fever and other allergies may become more sensitive to stimuli like pollen 24 hours after suffering a bout of stress.
The most common allergy treatments, such as antihistamines, generally had no effect on these delayed - or "late-phase" - reactions, which can in certain settings be life-threatening.
The researchers, led by professors at the Ohio State University, examined 28 seasonal allergy sufferers before and after exposing them to stress. In skin prick allergy tests they found the participants developed weals on their arms twice as big when highly stressed as when they were unstressed.
A day later they were still four times as likely to react more violently to the skin allergy test.
Study author Jan Kiecolt-Glaser, professor of psychology and psychiatry at the university, said: "What's interesting about this is that it shows that being stressed can cause a person's allergies to worsen the next day. This is clinically important for patients since most of what we do to treat allergies is to take antihistamines to control the symptoms - runny nose, watery, itchy eyes, and congestion.
"Antihistamines don't deal with those symptoms on the next day."