Naturally straight hair is primarily influenced by genetics, which determines the shape of hair follicles and the hair strand structure. Straight hair results from round follicles that allow hair strands to grow evenly and straight. Additionally, the way proteins, specifically keratin, are arranged within the hair strand also affects whether hair grows straight or curly. For straight hair, keratin is aligned symmetrically, giving it a smooth and flat texture.

Environmental factors like humidity, exposure to chemicals, or frequent heat styling can sometimes alter natural hair texture, but for those with inherently straight hair, it generally retains its sleekness. Many people who naturally have wavy or curly hair but desire the polished look of straight hair turn to straight hair extensions. These extensions offer an effortless way to achieve a straight style, adding length and fullness without the need for frequent heat styling, which can damage natural hair.