Final answer:
Hair coloring can be permanent, altering the hair structure, or semi-permanent, which washes out over time. Plant-based dyes like henna are natural alternatives, while some industrial dyes are not safe for hair use. There is no evidence linking the use of hair dye during pregnancy with an increased risk of birth defects.
Step-by-step explanation:
Hair coloring, or dyeing, is a process wherein the color of hair is altered for various reasons such as aesthetics, fashion, or to hide signs of aging like gray hair. The two main types of hair color are permanent and semi-permanent. Permanent hair color chemically alters the hair's structure by removing the natural color and replacing it with synthetic pigments, which stays until the hair is cut. Semi-permanent hair color washes out after several weeks, allowing the natural variation of hair color to show through, making the look more nuanced and maintaining the original hair texture longer.
For those seeking natural alternatives, plant-based dyes such as henna, indigo, and anthocyanin from blackcurrant skin are available. However, industrial dyes like Citrus Red 2 and Orange B are limited in use and not intended for hair. It's important to recognize that all pigments, whether natural or synthetic, will eventually fade, and the rate of fading depends on a variety of factors, including the molecules of the dye pigments themselves.
It is also worth noting that while some chemicals are associated with birth defects, there is no evidence that using hair dye during pregnancy increases such risks, a misconception that has been dispelled by studies.