An MS flare-up, also known as a relapse, attack, or exacerbation, is the occurrence of new symptoms or the worsening of old symptoms in multiple sclerosis. It can happen when inflammation in the nervous system damages the layer that covers and protects nerve cells, slowing or stopping nerve cell signals from getting to the parts of the body where they need to go. Symptoms of an MS flare-up usually come on quickly, over a period of hours or days, and can include eye inflammation, challenges with balance, fatigue, tingling, and numbness. To be considered a true relapse, symptoms must start at least 30 days after the last flare-up and stick around for at least 24 hours. MS flare-ups are different from pseudo-flares, which are temporary worsening of symptoms brought on by external factors and are not linked to new damage from MS. Common triggers for pseudo-flares include high body temperature from fever, infection, too much exercise, or activity, getting your period, new medications, and stress. It is important to talk to your doctor about any new or worsening symptoms to determine if they are a flare-up or pseudo-flare.