text: why do hot things burn me? i understand the biology behind burning and pain and i understand the purpose served by pain (to warn the body that something bad is happening to it and to pull away, reducing damage), but can anyone succintly explain the chemical/physical reaction that occurs to cause the actual burning of the tongue, finger etc? ok.  to start from basics  the human body is made up mostly of cells. cells are mostly microscopic bubbles of oil with salt water inside them. that accounts for 99% for what a cell is. the rest of the cell is the ‘important’ stuff that keeps the cell active and allows it to communicate and so forth.  and most of that stuff is protein.  a protein is a molecule comprising a chain of smaller molecules called amino acids. there are millions of different types of proteins, and they are the basic machinery of living organisms. proteins digest food, and they burn food to produce energy, they break down waste and move materials into and out of cells and they carry oxygen around the bloodstream. the chemical engines that make up muscles are proteins, so proteins are also entirely responsible for movement. basically if something changes inside the human body, proteins are responsible.  proteins also make up most of the structure in the human body. cells really are just bags of oil containing salt water, they have no structural integrity of their own. they rely on protein fibres both within the cell and between cells to allows them to maintain their shape. your body maintains it shape because of proteins.  so what happens when you get burned?  well the first thing that happens is that the proteins break down. the arrangement of the amino acids molecules gets shaken up and the proteins lose their shape, and without their shape they become non functional, useless. and because all the functions of a cell depend on proteins the cells themselves become nonfunctional. just as importantly the structural proteins break down and lose shape. that results in the cells and tissues losing their shape.   that breakdown of proteins is what is technically termed denaturation. the more common term is ‘cooking’. when we cook animals food we are largely trying to break down the proteins so that they are easier to digest. that is why cooked food is more tender than raw food, because the structural proteins have been smashed to pieces by the heat. a burn is nothing more or less than cooking of living tissue.  the first proteins to suffer from a burn are usually those on the surface of the cell. those proteins are either embedded in the cell membrane with one end sticking out, or they are just sitting on the surface waiting for molecules to come by to react with. either way, they cook.  the cooking of the surface proteins has one immediate effect: it disrupts water balance. those proteins were responsible for pumping water and salt in and out of the cell to maintain the correct balance. once they are damaged water and salts leak into and out of the cell at will.  the most noticeable effect of this is damage is in the formation of blisters. water, salt and even proteins leak freely into the damaged area because the proteins that are supposed to prevent it have been cooked into inactivity. we see that as a buildup of plasma under the skin: a blister.   the second thing that occurs if the heat is applied for long enough is that the cells rupture. they are after all just little bags of salt water. as soon as they heat up the bags rupture and spill their watery contents. if they are heated to over 100oc the water inside vaporises.  as a result the cells lose their shape and lose any ability to function. they die. now we have not just damaged leaking cells but dead and decaying cells. that presents a very real chance of infection if the area is large enough.  finally if the heat is applied for long enough and intense enough the structural proteins break down. the structural proteins are usually pretty tough, but they will cook eventually. when that happens the burned area loses its structural integrity. we can see this as the skin peeling off a serious burn. without the protein strands holding the skin together it turns into mush. if the heat is very severe the underlying tissue also suffer destruction of structural tissue and becomes a