Does bottling up anger cause cancer?

You have probably met this one. Someone says that people who swallow their anger, who never make a fuss, who put everyone else first, are the ones who end up with tumours. It gets repeated confidently, often by people who mean well.

The National Cancer Institute addresses the idea underneath it on its page of cancer myths. Asked whether attitude determines cancer risk or survival, NCI answers that there is no convincing scientific evidence that links a person's attitude to their risk of developing or dying from cancer.

There is no established emotional profile that produces cancer. The theory has been examined and has not held up.

Set aside the studies for a moment and look at what the claim requires you to believe.

It requires that a personality trait, present in an enormous share of the population, reliably produces a specific biological disease. Meanwhile the causes cancer researchers can actually document — tobacco, alcohol, certain infections, radiation, inherited gene changes, ageing itself — operate through mechanisms that have nothing to do with temperament.

Scale is the other problem. NCI notes that about 39 percent of men and women will be diagnosed with cancer at some point during their lives. Cancer is not rare enough to be explained by any particular character type. Loud people get it. Placid people get it. People who complain constantly get it.

If a trait were really driving cancer, it would have to be one shared by nearly four in ten people, which is not a personality at all.

It survives because it offers a promise disguised as a warning.

If unexpressed anger causes cancer, then expressing anger prevents it. That gives people a lever in a situation where they otherwise have none, which is exactly what fear wants. The same instinct produces the belief that positivity cures — the flip side of the same coin, and equally unsupported.

For families, blaming a personality also does quiet work. It explains why this person got sick and the rest of us did not. That is a comforting story for everyone except the person who is ill.

The damage lands on patients, not theorists.

People in treatment already carry enough. Being told that their nature invited the disease adds guilt to fear. Some then start policing their own emotions — hiding worry from family, apologising for a bad day, refusing to admit they are frightened — because they have been given the impression that feeling badly is dangerous.

Nothing in NCI's material supports that pressure. You are allowed to be angry about having cancer. You are allowed to be angry at the person who told you your anger caused it.

Talking about hard feelings is a good idea. Not as medicine, and not as prevention — as a way to be less alone with something enormous.

• Ask whether your treatment centre has a counsellor, psychologist or social worker.
• Consider a support group, where nobody needs the situation explained to them.
• Tell your team if your mood has changed. Low mood during treatment is common and treatable.
• Give yourself permission to be blunt with people who offer theories. A simple "that has been looked at, and it isn't true" is enough.

Your temperament did not cause this. Whatever you did or did not say over the years, in whatever tone, it is not the reason you are here.