ME/CFS causes and triggers
Key takeaways
Two different questions: what caused the illness, and what makes today worse.
Causes are usually a virus, physical trauma, or prolonged stress, often with a genetic predisposition.
Daily triggers include physical, cognitive, sensory, and emotional exertion.
Learning your personal triggers is the foundation of pacing. A daily activity and symptom log is the most reliable way to find them.
When trying to understand ME/CFS, it helps to separate two things.
What caused the illness to develop in the first place, and what triggers symptom worsening once you have it.
Medical science does not yet know the exact root cause of ME/CFS. Researchers do, however, know a good deal about how the illness typically begins.
What causes ME/CFS?
For most people, ME/CFS does not appear without a preceding event. It is usually associated with a significant health event that places severe stress on the body and immune system.
For some people there is no identifiable starting point, and the illness develops gradually. That does not make the diagnosis any less valid.
Viral infections
The most common starting point. ME/CFS frequently develops following infection with Epstein-Barr virus, which causes glandular fever, or with influenza or Covid-19.
Physical trauma
In some cases the illness follows a major physical event, such as a serious accident or significant surgery.
Prolonged stress
A sustained period of severe physical or emotional stress can sometimes act as a trigger, particularly in people who may already be vulnerable.
A genetic predisposition
ME/CFS runs partly in the genes. The DecodeME study, the largest of its kind, identified eight areas of the genome that differ in people with ME/CFS, linked to the immune and nervous systems.
This does not mean the illness is inevitable. It may mean the immune and nervous systems are more likely to respond abnormally after one of the triggers above.
Why this does not make ME/CFS psychological
Stress appearing on a list of triggers does not make ME/CFS a psychological illness.
DecodeME found no evidence that the eight ME/CFS genetic signals share common causal variants with depression or anxiety. The genetic picture points to immune and nervous system biology, distinct from psychiatric conditions.
Severe or prolonged stress has physiological effects on the immune system. That is the pathway being described here, not a state of mind.
What triggers daily symptom worsening?
Once ME/CFS has developed, the body’s energy system functions differently.
Activities that would not register as effortful for most people can trigger a significant worsening of symptoms, known as post-exertional malaise (PEM).
These triggers are not limited to physical activity. Cognitive and sensory exertion carry a real energy cost.
Physical and cognitive triggers
Physical exertion. Basic chores, showering, climbing stairs, or attending a medical appointment.
Cognitive exertion. Reading, working on a computer, managing finances, or sustaining a long conversation.
Sensory and emotional triggers
Sensory overload. Bright or fluorescent lighting, loud environments, or strong smells such as cleaning products or perfume.
Emotional stress. Arguments, difficult news, or significant emotional events, including positive ones.
Learning your limits
Triggers vary between people.
One person may be able to read for an hour but not stand long enough to wash up. Another may manage light physical tasks but find screen use quickly leads to a crash.
The most reliable way to identify your personal triggers is to keep a daily log of activities and symptoms. Patterns tend to emerge over several weeks.
Once you know your triggers, the next step is working within them. See the pacing guide for how to do that.
Related pages
What is ME/CFS?
A plain-language introduction to the illness and how it starts.
Post-exertional malaise (PEM)
The delayed crash that follows activity.
Pacing guide
How to work within your energy envelope.
ME/CFS symptoms
The main symptoms explained in plain language.
How ME/CFS is diagnosed
What doctors look for, and what to expect from the process.