Turmeric stains turn red when soaked in detergent due to a chemical reaction between the curcumin in turmeric and the alkaline components of the detergent. Curcumin is a yellow pigment that is responsible for the characteristic color of turmeric. When curcumin comes into contact with an alkaline solution, such as a detergent, it undergoes a chemical change called "alkaline hydrolysis." This process causes the curcumin molecule to break down and release a red-orange compound called curcuminoid. The curcuminoid is what gives the turmeric stain its red color.

The alkaline hydrolysis of curcumin is a relatively slow process, which is why turmeric stains can sometimes take a while to turn red. The rate of reaction also depends on the concentration of the detergent and the temperature of the water. Hot water will speed up the reaction, so if you're trying to remove a turmeric stain, it's best to use hot water and a detergent that contains an alkaline component.

Once the turmeric stain has turned red, it can be difficult to remove. However, there are a few things you can try. One option is to use a stain remover that is specifically designed for removing turmeric stains. Another option is to make a paste out of baking soda and water and apply it to the stain. Let the paste sit for several minutes, then rinse it off with water. You may need to repeat this process several times to completely remove the stain.