Researchers are yet to identify the reason behind the sudden change of hair texture. But it’s likely due to the unique combination of genes, hormones, and aging. Now that you already know that hair can actually change over time, the next question is when can straight hair become naturally wavy without a stylist? Puberty The first major shift in our hormones is when we hit puberty. A teen hitting puberty can easily see the changes in their body by simply looking at the mirror.