ME/CFS causes and triggers
When trying to understand ME/CFS, it helps to distinguish two separate things: what causes 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 to start?
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.
- 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.
- Viral infections. The most common starting point. ME/CFS frequently develops following infection with Epstein-Barr virus (which causes glandular fever), influenza, or COVID-19.
- Physical trauma. In some cases, the illness follows a major physical event such as a serious accident or significant surgery.
The genetic factor
Research suggests some people may have a genetic predisposition to ME/CFS. This does not mean the illness is inevitable — but it may mean that their immune and nervous systems are more likely to respond abnormally when exposed to one of the triggers above.
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.