What Is an MS Relapse?

Reviewed by: HU Medical Review Board | Last reviewed: March 2024 | Last updated: March 2024

Multiple sclerosis (MS) is a disease of the central nervous system (CNS). The CNS includes the brain, spinal cord, and some of our nerves. It controls everything we do.1

There is still much to learn about MS. But experts have found that MS is caused by the immune system attacking the central nervous system, including the brain.1

What is a relapse in MS?

The most common type of MS is called relapsing-remitting MS. This is when the symptoms of MS seem to suddenly come and go in episodes. The relapse is the period when symptoms are present or worsened. The remission is when symptoms stay the same, improve, or go away..2,3

Relapses can last a few days, a few weeks, or even a few months. Symptoms can appear over a few hours or days. The symptoms may be the same as previous relapses or may be in different areas of the body or of different severity. People living with MS may also call relapses "attacks" or "episodes."2,4

According to the National Multiple Sclerosis Society, true relapses that represent new damage from the immune system attacking the central nervous system:4

  • Last at least 24 hours
  • Happen at least 30 days after the last relapse
  • Happen because of MS and not another cause (such as an infection)

Relapses can happen in other types of MS, such as secondary progressive or primary progressive MS. But relapses in these types of MS are less common.2

Symptoms of relapses

Every person with MS experiences different symptoms during relapses, depending on where the immune system attacks. Even for the same person, each relapse may feel different. Relapses can cause optic neuritis, fatigue, or difficulty with balance.4

Experts sometimes separate relapses into 5 categories. These are:2

  • Optic neuritis – blurred vision in 1 or both eyes or changes in your vision caused by inflammation of the nerves of the eyes
  • Sensory relapse – changes in sensations like pain or “pins and needles” in one or more areas of the body
  • Motor relapse – weakness in one or more parts of the body
  • Cognitive relapse – changes in thinking or memory, like brain fog
  • Mixed relapse – symptoms from multiple categories occurring at once

Symptoms are likely to worsen over the first few days of a relapse. They will then often plateau, or stay the same for a while, before slowly easing. Some symptoms may get better quickly. But it is possible to have symptoms that take up to 6 months to fully get better. In some cases, relapse symptoms may not fully improve and some degree of symptoms may persist long-term.2

What happens during an MS relapse?

Immune cells travel in the blood to all areas of the body. These cells defend the body from outside attackers like foreign bacteria or viruses. In autoimmune diseases like MS, the immune cells are confused. The immune cells attack healthy cells in the body, thinking these healthy cells are intruders. In MS, immune cells specifically attack myelin.2

Myelin wraps around nerves and helps the nerve send messages quickly, much like insulation on a wire. When the immune cells attack and cause inflammation, the myelin is broken down. This means the nerves cannot send their messages as quickly. Sometimes, the nerves cannot send messages at all. And sometimes, the nerves themselves are damaged and destroyed. These areas of myelin breakdown are called lesions. An MS relapse occurs because of this inflammation.2

Myelin can sometimes repair itself to some extent during a process called remyelination. However, the new myelin is not quite as thick as the original myelin. In many cases, nerves remain demyelinated even after the inflammation has resolved. Failed remyelination and poor remyelination are why some symptoms may not fully go away.2

What can cause symptoms similar to relapse?

It is possible for your old MS symptoms to temporarily worsen outside of a relapse. This phenomenon is called a pseudo-relapse, "exacerbation," or "flare-up."2

Pseudo-relapses occur when previously demyelinated and damaged nerves are stressed and unable to communicate properly. This process causes symptoms to temporarily return or worsen. This worsening of old MS symptoms can be caused by:2

  • Infections
  • The temperature
  • Stress or tiredness
  • Your menstrual cycle


Colds, urinary tract infections, and cases of stomach flu can worsen your old MS symptoms. In rare instances, severe infections may even cause a new relapse.2

Extreme temperatures

Some people with MS have temperature sensitivity, and extreme temperatures, particularly extreme heat, can trigger or worsen their symptoms.2

Stress and tiredness

These can both be difficult to avoid. But it is important to try to manage your stress and get enough sleep. High stress and poor rest can both worsen your symptoms.2

Menstrual cycle

Some people find that their prior MS symptoms return or worsen in the days before their period starts. These symptoms often improve once the cycle has started (menstrual bleeding begins for the cycle).2

What should you do if you experience a relapse?

It may help to keep track of your MS symptoms so you can better understand your MS relapses.2

If your symptoms are mild and consistent with old relapses or you think they are caused by other factors like the ones listed above, you may want to wait to call your doctor.2

But if your symptoms are interfering with your life, are not the same as any prior relapses, or if you are concerned about them, reach out to your doctor. They will be able to answer your questions and can help determine if you need treatment.2

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