It’s cold and flu season. That means you’re very likely surrounded by a symphony of coughs and sniffling noses — if you’re not actively coughing yourself.
And whether your main complaint is a cough, a fever, a headache or a runny or stuffy nose, you may notice that you tend to feel worse at night.
That’s not your imagination. Several factors are to blame, starting with your circadian rhythm, which is your body’s internal clock. When the sun sets, it tells your brain to wind down for bed and, at the same time, spurs certain immune cells to become more active. Every night, those cells are recruited to different parts of your body, on the lookout for invading pathogens like viruses and bacteria.
“When they identify and try to fight off viruses, the immune cells can cause irritation and inflammation, which ends up making respiratory symptoms worse at night,” said Dr. Diego Hijano, a pediatric infectious disease specialist at St. Jude Children’s Research Hospital.
Certain hormones, like cortisol, also follow a circadian rhythm. Cortisol levels are highest in the morning, which may help suppress inflammation during the day and, in turn, tamp down symptoms. As cortisol levels begin to fall in the evening, symptoms may start to flare up again.