Cotton shirts seem to be particularly susceptible to getting a yellow discolouring under the arms. This can be avoided if you make a paste out of bicarb soda and water, spread it over the stain and leave for an hour or two. This should remove the stain, unless it has been there for a long time and ironed into place. Another trick is to spray under the arms of cotton shirts with distilled white vinegar each time the shirt goes in to the wash.
- Bicarb soda
- Distilled white vinegar