Simplify the following text for a Grade 5 native English-speaking person.
Original: Hair straightening is a hair styling technique which involves the flattening and straightening of hair in order to give it a smooth , streamlined , and ` sleek ' appearance . It may be accomplished by using hair irons and hot combs , chemical relaxers , Japanese hair straightening , or Brazilian hair straightening .
Simplified: Hair straightening is when a person makes their hair straighter .