发作 (fā zuò): to flare up; to break out

He has epilepsy, which tends to flare up when he gets emotional, so his family always tries to keep him calm.

Her stomach problem flared up again, and the pain made her break out in a cold sweat, so she had to ask for leave and go home to rest.

Every spring, his hay fever flares up; his eyes become red and itchy, and he sneezes nonstop.

After hearing the bad news, his heart condition suddenly flared up, and he was rushed to the hospital for emergency treatment.

This skin condition flares up every summer; the doctor advised him to get less sun and keep his skin dry.