The duration that hair straightening lasts can vary depending on the individual’s hair type, maintenance routine, and the specific straightening method used. Generally, temporary methods like flat ironing or blowouts might last for a day or until the next wash, while semi-permanent treatments like keratin treatments could keep hair straight for a few weeks to a couple of months. For a longer-lasting effect, you might consider permanent straightening techniques such as Japanese or Brazilian straightening, which can last several months, often until new hair growth becomes noticeable. Proper aftercare, including the use of appropriate hair products and regular touch-ups, can extend the duration of your desired straightened look.