🚀 go-pugleaf

The redness and whiteness during light burns is the result of different
behaviour of the subcutaneous capillaries.

Heat induces shock.

The resident granulocytes (histiocytes residing in the subcutaneous tissue)
degranulate, and among others release histamine that is a potent
vasoconstrictor. It causes the smooth muscle in the capillary to constrict.
Constricted blood vessels reduce the blood flow locally, and the skin looks
pale (white). This reaction is less visible in the more pigmented skin.

Now if the burn is more severe, is causes tissue damage. Cells necrotize and
the permeability of endothelial lining of the blood vessels increases
(serum exudes)  in addition to the histamines other components are released
too including the components of the complement system, all of this results
in a localized, but rapidly escalating inflammatory reaction. This further
increases the vascular permeability, vasodilation and enhanced blood  which
is necessary for leucocytes to infiltrate the damaged tissue (to protect and
help to repair it).

At this stage erythema formation is common occurrence which is the swelling
and redness of the affected areas of the skin. This takes some time to
develop, so the proper order of changes is: whiteness immediately after the
injury, followed by redness in minutes or hours.

Now if you have a VERY strong burn, "cauterizing" burn, that coagulates 
proteins even deeper in the tissue, it plugs the blood vessels by causing 
the proteins to coagulate, there is no blood circulation, and the skin 
remains pale (white). Because of reduced circulation, it takes much longer 
for the inflammatory reaction to begin and usually the injury develops a 
decently sized "sack" filled with yellowish plasma that hides any color 
below it (plain optical phenomenon) it  protects the underlying tissue but 
dries up gradually and normal blood coagulation proteins help to form a 
brownish cover over the damaged area.

The ultimate burn injury results in charring. Charred tissue is initially a 
dry mixture of skin proteins and blood, contains large amount of 
carbohydrates, lipids, hemoglobins etc, and all kind of degradation products 
thereof, carbonized,  caramelized sugars etc, that causes it to have a dark 
almost black color. It never regenerates (dead tissue), but easily breaks 
and allows bacteria to seep into the wounds. charred tissue is usually 
removed to hasten the healing.

lajos