The collar and cuffs of shirts are extremely stained and difficult to wash. You can evenly apply some toothpaste on the collar and cuffs, gently brush with a brush, and then rinse it with clean water to remove stains.
Dip a small brush in dishwashing liquid, brush it onto the stains on the collar and cuffs (don’t be too much, just see wet), and then put the clothes in the washing machine to remove dirt. If you wash it by hand, you will get the same effect.
Sprinkle some salt on the collar, rub it gently, and then wash it with soap. Because most people's collars are soaked in sweat, which contains protein and dissolves quickly in salt solution. If it is still not washed clean, you can also wash 1 part of ammonia water and 4 parts of a desalinated ammonia aqueous solution.
Wash the collar of the shirt, and you can also take 50 ml of anhydrous alcohol and put it in 100 ml of carbon tetrachloride, fill it in a sprayer and spray it evenly on the dirty spots. Use a brush to wipe it off, and the dirt can be removed. After the liquid evaporates, put the shirt into the washing machine and wash it according to routine to obtain a satisfactory cleaning effect.