I don’t wear T-shirts much anymore, but a lot of my older T-shirts have built up this hard, crusty residue in the armpits, almost definitely due to deodorant. I’m sorry if this sounds gross, but the shirts are clean and smell just fine. These areas are just stained (usually white T-shirts are discolored yellow around the pits), and sometimes the fabric just gets stiff and hard. Is there anything I can do about this, or are they just destined to be undershirts from now on?
FWIW, I’ve changed my deodorant since then, but I’ve owned most of these T-shirts for several years.
Roll on deodorants require a carrier gel for the active ingredients. In many cases the carrier includes long chain hydrocarbons, alcohols and the like. Right-Guard gel for example contains Stearyl Alcohol, PPG-14 Butyl Ether, Hydrogenated Castor Oil, and Myristyl Myristate. These compounds are all susceptable to oxidation and polymerization when exposed to air.
When linseed oil polymerizes on a fine piece of furniture, it turns a little yellow, becomes hard and insoluble, and leaves the wood with a nice finish. When Hydrogenated Castor Oil polymerizes on a T-Shirt, it turns a little yellow, becomes hard and insoluble, and leaves you in need of a new shirt.
I’ve had good results with using Spray and Wash stain stick on the affected area then, after that sits for at least a day, pouring boiling water through the fabric and washing the shirt as usual.
When I get a new shirt I try to use the stain stick routinely on it before any build up occurs.