What is Uhthoff’s Phenomenon?
Uhthoff’s phenomenon is a temporary worsening of existing MS symptoms caused by an increase in body temperature. It is not a relapse and does not cause new damage. Symptoms usually improve once the body cools down.
Why Heat Affects MS
MS damages the protective covering of nerves (myelin). Heat makes these damaged nerves conduct signals less efficiently, leading to temporary symptom flare-ups such as fatigue, weakness, blurred vision, balance issues, and brain fog.
Common Heat Triggers
- Hot or humid weather
- Fever or infection
- Physical exertion
- Hot showers or baths
- Stress and dehydration
Why Summer Can Be Difficult
Even a small rise in body temperature can worsen symptoms for some people with MS. This may lead to reduced mobility, increased fatigue, and anxiety around daily activities.
Practical Tips to Stay Cool
- Spend time in shaded or air-conditioned spaces
- Use cooling towels, neck wraps, or vests
- Take cool (not icy) showers
- Stay well hydrated
- Pace activities and rest often
- Wear loose, breathable clothing
Important Reassurance
Uhthoff’s phenomenon is temporary and reversible. If symptoms last longer than 24–48 hours, or feel different from your usual MS symptoms, contact your healthcare provider to rule out a relapse or infection.
👉 We encourage members to also read this article on understanding the difference between a flare and a relapse: https://www.healthline.com/health/multiple-sclerosis/difference-between-ms-flare-and-relapse