Have you ever noticed your skin flaring up before a big event? Scientists have linked stress to worsening allergies, but the biology behind it was unclear—until now.  Japanese researchers have identified the cellular chain reaction linking stress to worsened skin allergies.  Researchers discovered that under stress, immune cells called macrophages, which usually reduce inflammation, lose their ability to function properly.  These cellular changes can persist for up to a week after stress, potentially explaining prolonged allergy symptoms during stressful periods. During stress, the sympathetic nervous system releases norepinephrine, which weakens macrophages' ability to reduce inflammation by impairing their cleanup of dead cells. "Our findings suggest that the impact of psychological stress on immune cells is long-lasting and can even affect macrophages that differentiate later. This phenomenon, referred to as ‘stress memory,' implies that severe stress leaves a lingering imprint on immune cells," explained Soichiro Yoshikawa, Ph.D., from Juntendo University. As scientists explore potential treatments, the findings highlight that stress management is not just beneficial for mental health but also crucial for immune function.