Thermal styling and heat safety

Every question in this area rests on one piece of chemistry: heat styling works on hydrogen bonds, and hydrogen bonds are broken by water. That single fact explains why the set is temporary, why humidity ruins it, and why the iron only goes on dry hair.

Why a wet set is temporary	It works on hydrogen bonds, and water breaks them again
Why a set collapses on a humid day	Moisture in the air re-breaks those same bonds
A thermal iron	Used on completely dry hair
Testing iron temperature	On a piece of tissue or a damp cloth, before it touches the client
Chemically relaxed hair	A lower temperature than virgin hair of the same texture
Working close to the root	A heat-resistant comb between the iron and the scalp
Blow-dryer airflow	Downward, from scalp toward the ends
Why section for a blow-dry	So each part is fully dried and smoothed before moving on
Daily heat styling	Cumulative cuticle damage that weakens the strand

Where the point is lost: The downward airflow question has a reason behind it worth carrying into the exam: aiming the dryer from scalp toward the ends lays the cuticle scales flat in the direction they already lie, and flat scales are what reflect light. Directing air up the strand lifts those scales, which is why the same client with the same product can leave looking rough one day and smooth the next.