Uhthoff's Phenomenon

What it is

Uhthoff's phenomenon is when MS symptoms temporarily get worse as your body heats up. Triggers can include hot weather, a hot shower, exercise, or a fever. Symptoms usually settle back down once you cool off.

What you might notice

Blurred vision, heavy legs, or returning fatigue during hot weather, after exercise, or in a hot shower. Usually fades within an hour of cooling down.

Why it matters for you

If vision blurs or legs feel heavier in the heat, the change can have a name. Knowing this name helps separate heat-related symptom return from the language used for a true relapse.

Questions to ask your doctor

• Has this lasted more than 24 hours?
• Could this be a pseudo-exacerbation (heat, infection, stress)?
• Should I come in for an exam?
• Would steroid treatment help?
• Should I go to the ER?

Related terms

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