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The Law of Dual Effect

By on May 18, 2017 in Health, Information, Science | 0 comments

hot or cold

In February, Henna outlined the basics of applying hot and cold to the body as treatment.

Today, I want to introduce you to the next level.

Primary Effect

Initially, when you apply heat to the body, all the small blood vessels open to increase circulation. This is part of the mechanism the body uses to regulate temperature. Conversely, putting cold on the body makes the capillaries constrict, reducing blood flow.

These are primary effects and last up to one or two minutes, before the secondary effect is triggered.

The secondary or ‘dual’ effect is the opposite to the first.

Secondary Effect

After removing a heat pack or getting out of a hot shower / bath, within a few minutes, the circulation starts to reduce. Blood vessels start to narrow again and the affected area can be subject to reduced blood flow for up to half an hour before the body returns to normal.

After exposing the body to cold, the circulation floods back into rapidly dilating capillaries. The body maintains higher blood flow in the area for up to 30 minutes after removing the cold.

Best Practice

When treating any injury, I always recommend using ice to begin with. Applying ice or cold packs to the area in one minute periods, repeated five times with one minute gaps (see here) is the best initial treatment.
This helps to reduce pain, improve circulation and clear inflammation.

Once the pain is under control and movement is much easier, using alternate hot and cold helps to pump the blood through the area. This helps to take the body to the next stage of healing.


Ice packs / cold packs are an invaluable tool for rehabilitating after injury and the first anyone should turn to. When significant progress is being made, switch to alternate hot and cold compresses / contrast bathing.

Heat always feels nice but will hurt in the end once you take it away. Cold may be a bit of a shock to begin with but you will feel the benefit much more afterwards.

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