Stress comes from many different sources, but as a chiropractor what I find most intriguing is not what causes stress, but what goes on in the body when we're subject to it.
Stress is not a purely psychological phenomenon. Chemical and physical changes take place in our bodies within seconds of a stressful stimulus.
A short term stress response (such as occurs immediately after being wounded on a battlefield) is very noticeable; a quickening heart rate, sweating, faster breathing and so on.
In essence, these changes are to prepare the body for action, to help get you out of trouble.
With this in mind, the short term influence of stress on pain is very easy to understand.
When in a battlefield situation, stress supresses pain.
But what about the muddy effects of chronic stress? The type of stress that occurs if your boss is subjecting you to month after month of objectionable misery, or when a family member has been given a diagnosis like dementia.
Initially, the effect is the same as in our soldier. But your body can't keep going indefinitely like that; sweating copiously, not digesting things and breathing at twice its normal rate.
The longer stress continues, the more the clear and obvious signs fade, and the more our internal chemistry starts to alter.
These internal changes affect how pain is perceived.
As well as the expected heightened emotional response to pain when we are under chronic stress, physiological changes increase our sensitivity to pain.
This increased sensitivity, resulting in a lower pain threshold, is largely down to increased production of a chemical called Substance P.
Substance P is a neurotransmitter, helping nerves communicate, but it has more effects than that.
Substance P can increase the excitability of pain-carrying nerves, and can contribute to inflammatory processes (another important influencer of pain).
In summary, short term stress is a great pain killer, but long term stress will make pain more painful. A bit of a problem if that stress is caused by chronic pain...