"Period Flu," Endometriosis, and the Weather: What's the Connection?

A woman gazes thoughtfully out the window, watching raindrops gently trail down the glass on a gloomy day.

If you live with Endometriosis and feel like your symptoms flare up when your period comes, especially alongside body aches, chills, fatigue, or even feeling like you’re catching the flu — you’re not imagining it. Many patients call this phenomenon “period flu.” And for those navigating life with Endometriosis, this experience can be even more intense.

Add in the fluctuating Canadian weather, and you’ve got a perfect storm.

Let’s unpack what’s going on.

What Is “Period Flu”?

“Period flu” isn’t a medical diagnosis, but it’s a term that’s become widely used in online communities and patient circles to describe the cluster of symptoms that show up during the menstrual cycle and mimic the flu.

• Muscle aches

• Low-grade fever or chills

• Nausea or digestive upset

• Extreme fatigue

• Mood changes

• Brain fog

  
  

It’s not a viral infection, it’s your immune system reacting to the hormonal and inflammatory shifts that happen during your cycle.

Why It’s Worse with Endometriosis

For those with Endometriosis, inflammation is already a major issue. Endometriosis is a chronic condition where tissue similar to the uterine lining grows outside the uterus, causing pain, inflammation, and often immune dysregulation. During menstruation, these misplaced cells respond to hormonal changes, leading to even more inflammation and immune activation.

So when people with Endo talk about feeling like they’ve been “hit by a truck” during their period — that’s real. It’s not just the cramps or fatigue — it’s a full-body reaction.

And for some, the immune system’s heightened response can bring on symptoms that feel flu-like: feverish sensations, body aches, and overwhelming fatigue.

Weather Whiplash: Why Changes in Temperature Might Affect You

Here in Canada, we know a thing or two about drastic weather changes. One day it’s sunny, the next it’s snowing in April. And for many people with Endometriosis, shifts in weather — especially sudden drops in temperature or damp, cold days — can increase pain sensitivity and fatigue.

There are a few theories why:

Barometric pressure: Sudden drops in pressure (often before a storm or cold front) have been linked to increased joint and nerve pain. This might worsen pelvic or referred Endo pain.

Temperature shifts: Cold weather may increase muscle tension and cramping, especially in the pelvic region.

Sunlight and vitamin D: Less sunlight in colder months may contribute to fatigue and mood changes, which are already common during flares.

Living with Endometriosis means learning to anticipate your body’s rhythms — and yes, that includes the weather.

Here are a few strategies that may help:

• Track your cycle and symptoms: Apps or journals can help you spot patterns — like when “period flu” symptoms tend to strike or how weather changes affect your pain.

  
  

• Layer up and stay warm: Heat therapy (heating pads, warm baths, heat patches) can help soothe muscles and reduce cramping

  
  

• Hydration and rest: During your cycle, give yourself permission to rest more. Drinking water, eating anti-inflammatory foods, and getting extra sleep can support your immune system.

  
  

• Talk to your doctor: If your “period flu” is severe, bring it up with your healthcare provider. You may benefit from adjusting your treatment plan or exploring hormonal or immune-related supports.

  
  

You’re Not Alone.

At Endometriosis Canada, we hear from people across the country who are navigating this complex mix of Endo, immunity, hormones, and the weather. Your experiences are valid, and support is available.

Have you experienced period flu? Does the weather affect your Endo symptoms? Join the conversation in our Facebook Support Group and share your story.