Once a burn has cooled (with water or not), does further submersion in cool water help?

Question

The standard treatment for burns seems to be to put the burn in cool water for 10 to 20 minutes.

It seems sensible to me that some burns can gain a benefit from this action when the skin/flesh is still extremely hot and is essentially still cooking from the residual heat. For example, if a hand was dipped in a deep fryer, putting it immediately into cool water would be a great idea as it will immediately start to cool the the flesh. The burnt flesh for such a case may initially as high as 180 degrees C and clearly needs to be cooled as soon as possible to prevent deeper flesh getting burned.

I'd guess that the temperature at which cells in your body are damaged is probably in the range of 45 to 55 degrees. Once the temperature of flesh drops below that point (whatever it may be), perhaps there is no further benefit in cooling the burn, except perhaps for comfort.

A less severe burn caused by hot water (lets say 75 degrees C) would cool much more quickly by itself (in dry air anyway) thanks to the evaporation of the water (unlike a burn caused by hot oil), and if submerged in cool water would cool to an acceptable temperature within just a few seconds. Is there really any benefit to leaving it in cool water for 10 minutes or more?

If my understanding is correct, there is also a reduction in pain when a burn is not exposed to air. Presumably this is the reason why wrapping with plastic cling wrap (after applying cool water) is recommended by some for reducing the pain from a burn. I think this effect would also intuitively cause people to think that submerging the burn is giving benefit, when perhaps it isn't.

Answer 1

The recommendations in this area vary, and the science they are based upon seems to be not entire resolved, but there's enough evidence to give practical recommendations.

The Australasian Cochrane Centre published an Evidence Summary for the Early Cooling of Burns where they looked at a number of studies in 2009, including a systematic review that looked at 42 more.

They concluded (emphasis mine):

Immediate cooling of burns is effective and safe at reducing the severity of tissue damage and relieving pain. Optimal duration and temperature of cooling is unclear, although animal studies have suggested that burns should be cooled immediately in running tap water for at least 20 minutes.

Meanwhile in 2010, another study looked at the existing research:

• Cuttle L & Kimble R, First aid treatment of burn injuries, Wound Practice and Research 6 Volume 18 Number 1 – February 2010

They discuss the evidence:

Previously there has been a lot of conflicting information in the literature regarding the optimal duration and delay of first aid treatment. As first aid treatment is often applied only to relieve pain, the preferred duration of the treatment may be until no pain is felt on removal of the cold – which can be for up to several days! However, researchers have recommended durations of 30 minutes, 2 hours, or 30 minutes – 3 hours. Recently, Bartlett et al found that tap water treatment of porcine burns for 20 minutes showed statistically less histological damage 9 days post-burn compared to 5, 10 and 30 minutes duration. This is in agreement with our own studies which showed that wound re-epithelialisation was faster (p=0.05) after 20 minutes of first aid treatment compared to untreated controls. Interestingly, for both studies, longer durations of first aid treatment (30 minutes or 1 hour) did not provide any further benefit, perhaps indicating that first aid should only be applied for 20 minutes and if pain persists after this time, other analgesics such as paracetamol should be administered

Finally, they conclude with an updated set of recommendations for the public, which include:

Treatment: Cold running water
Temperature: Tap water (2-15°C)
Duration: 20 minutes is best, 10 minutes - 1 hour is acceptable
Delay: Immediate is best, 1-3 hours is acceptable

(This is a summary, there is also important advice provided about when to seek emergency treatment.)