It's really very simple. It's caused by the action of the blade over your skin. But more specifically if you use the wrong angle and/ or apply too much pressure. With folks starting out with a straight it can be due partially to you skin being accustomed to the new shave method. Certain strokes seem to bring it on like ATG. Also doing too many strokes over the skin can bring it on as can using a dull razor.

Of course added to the mix would be individual skin sensitivities and skin conditions.

I've never found any product that really neutralizes or prevents severe burn. Probably the best product I've found is the Thayers medicated Witch hazel.