Stains on the collar of your shirt are caused by perspiration and the transfer of natural body oils as well as oil from skincare products. Perspiration contains proteins and urea which contribute toward yellow discolouration on the collar or armpit area of shirts. It's important to remove these collar stains before the garment goes into the dryer since heat causes the stain to set. It's best to remove collar stains with remedies that get rid of both odour-causing bacteria and stain-causing proteins.
Lay the shirt on a flat work surface with the inside of the collar facing up. Wet a clean sponge with ammonia and blot the collar stain to remove any discolouration caused by perspiration and body oils.
Mix 4 tbsp baking soda and 1/2 cup warm water in a bowl. Work the baking soda paste into the collar with an old toothbrush. Leave the paste on the fabric for 10 minutes to remove stain and odour.
Flush the collar with warm water to rinse off the baking soda paste and assess the stained area. Rub enzyme pre-soak stain remover into the collar if any stain is left. The enzymes in the stain remover break down proteins from sweat, helping to remove stains and odours.
Launder your garment with detergent. Check the shirt to make sure the entire collar stain is removed before placing the garment in the dryer. Heat from the dryer can cause the stain to become permanent.
Add 1 cup white vinegar to the wash cycle to boost stain-removing power and remove odours. Soak your shirt for 30 minutes in 1 gallon cool water and 1/2 cup oxygen bleach to remove stains. Sponge old stains on the collar with white vinegar instead of ammonia. This helps to lift yellow discolouration from the fabric.