* Sun Exposure: Sunlight can break down the dark pigment (eumelanin) in brown hair, leaving behind the red and yellow pigments (pheomelanin) that are also present. This can make the hair appear reddish or bronzed, especially in the summer.
* Chlorine: Similar to sun exposure, chlorine in swimming pools can strip away the darker pigments in the hair, making the red tones more visible.
* Genetics: Some people with brown hair naturally have more pheomelanin (the pigment responsible for red and yellow tones) in their hair. While the overall color might be brown, the underlying red tones can become more noticeable under certain conditions.
* Hair Products: Certain shampoos, conditioners, or styling products can contain ingredients that enhance red tones in the hair.
* Oxidation: Exposure to air can cause the eumelanin in brown hair to oxidize, leading to a slight lightening and potentially revealing red undertones.
* Age: As people age, their hair can lose some of its melanin, which can result in the appearance of more red tones.