Blonde hair turning green after swimming is often attributed to the interaction between the hair and chemicals in the pool water, particularly chlorine. Chlorine, commonly used to sanitize swimming pools, can react with certain minerals, such as copper, that may be present in your tap water or in hair products.

When chlorine combines with copper, it forms copper chloride, which has a greenish color. This compound can then bind to the protein in the hair, especially if the hair has been damaged or has open cuticles from bleach or exposure to the pool water, leading to a greenish tint. This effect is more noticeable on blonde hair because it lacks the darker pigments that might mask the greenish hue.

To prevent this, it’s helpful to rinse your hair with clean water before swimming to reduce the absorption of pool water, and to use hair products designed to protect against chlorine damage.

Additionally, wearing a swimming cap can provide a physical barrier to reduce exposure to pool water.