Cotton once wet will take days to dry and it breathes poorly. I used to deliver sailboats to the Caribbean and with cotton shirts I got skin sores from the damp material. Cotton is OK for casual use pants but not for shirts or socks.
I go with 100% synthetic for shirts and the best brands I have found are Moose Creek and Redington. They use high quality fabric and buttons and are sewn properly. Some have underarm zippered vents and others us a rear vent underneath the shoulder yoke.
I treat them with permethrin myself and so can have the exact strength needed for 12 months of bug protection. This strength of 1% also lasts through more than 50 washings. It costs me about 5 cents per item to treat it as compared to paying an additional $10 to $15 for a pre-treated shirt.
When traveling these shirts can be hand washed and will be dry in the morning, even in the tropics with high humidity.
What makes people sick has primarily been flame proof chemicals put on fabrics which was all a con created by a fellow that bought the company producing the chemical and needed a large market. He got gullible legislators to create laws forcing furniture and pajama manufacturers to use his flame retardant.
