The fabric contacted by the zipper of the new dress turns red.

Clothing fabrics contain fluorescent dyes or reactive dyes residues.

1. The fabric of clothes contains fluorescent dyes, which are used in the fabric dyeing process. Metal ions on the surface of zipper copper teeth are not thoroughly cleaned or the components in the cleaning solution remain. When the zipper is tightly pressed on the cloth, the metal ions react with the fluorescence in the cloth, which causes the cloth to turn red.

2. Clothing fabrics also contain reactive dyes, and substances such as soda ash will remain in the dyeing process. When the zipper comes into contact with the fabric, these residues will react with the dyes in the fabric, causing the fabric to turn red.