Can Swimming Pool Shampoos Truly ‘Remove’ Chlorine?
If you enjoy swimming, you have likely heard of "swimming pool shampoos," commonly known as "de-chlorinating shampoos." Frequent swimmers often experience hair that becomes discolored, brittle, or coarse. Swimming pool shampoos emerged as a solution to these issues and have been widely used ever since. However, many people only have a vague understanding of their actual mechanisms and effectiveness.
What exactly is a swimming pool shampoo?
Swimming pool shampoos typically contain "anti-chlorine" ingredients. The most representative ones are Sodium Thiosulfate and Vitamin C (ascorbic acid or its salts). These substances are originally reducing agents used to eliminate chlorine from water. The basic concept of these shampoos is the application of chemicals used for chlorine neutralization in water treatment or laboratory settings to a personal care product.
The Principle of De-chlorinating Shampoos
Sodium Thiosulfate is a powerful reducing agent that triggers an oxidation-reduction (redox) reaction upon contact with chlorine, converting it into a relatively stable chloride (Cl¯) form. Vitamin C acts in a similar manner to neutralize chlorine. These chemical reactions are well-established, and the term "chlorine removal" stems from this scientific principle.
But can it really remove chlorine from hair?
There is a point to clarify here. While there is extensive research on the chemical neutralization of chlorine, there is limited research specifically investigating how these ingredients perform on human skin or hair. In other words, while the chemical principles are clear, quantitative studies demonstrating their efficacy on hair follicles remain limited.
To what extent is chlorine removed?
It is chemically feasible for Sodium Thiosulfate or Vitamin C to access and trigger a reduction reaction with "free chlorine" existing on the hair surface or chlorine that is relatively weakly attached. However, while these ingredients neutralize chlorine, they do not repair the hair protein structures that have already been damaged by chlorine exposure. Furthermore, it is important to note that free chlorine itself can be rinsed away with plain tap water.
The Misconception: "Chlorine remains in the hair and causes continuous damage"
The common claim that "chlorine stays in your hair and continues to damage it" is not entirely scientifically accurate. Chlorine is highly reactive; it either disappears after reacting with the hair or is washed away by water. Hair damage worsens not because chlorine "lingers" indefinitely, but rather because of the cumulative damage from repetitive exposure during swimming, or because the contact time is extended when hair is not rinsed thoroughly after a swim.