First, why conventional cotton undies are bad...
They are processed with chlorine bleach & hydrogen peroxide & formaldehyde is also applied in the processing of the fabric.
Dioxin is a carcinogen derived from chlorine bleach & is responsible for hormone disruption.
The dye process also has heavy metals that contain harmful carcinogens.
Conventional cotton production account for more than 10 percent of pesticides used & 23 percent of agricultural insecticide sales.
Contamination of ground water is directly linked to pesticide & fertilizer use on cotton crops. Nitrates found in these fertilizers are found to cause "blue baby syndrome" in infants.
Use of chemicals in processing makes the fibers weaker & therefore wear out faster.
Now the good news...
Organic cotton doesn't use any synthetic fertilizers or pesticides.
Growing the crop organically doesn't damage the soil, environment or human health.
Organic cotton farming doesn't poisen farm workers or their families.
No GMO (genetically modified) is allowed in organic cotton.
Organic cotton is stronger due to the lack of chemical processing.
So what do you want to put next to your body? I know you are saying "But it is more expensive than regular underwear". Okay, good point. I understand that. But if you are buying cigarettes or eating fast food, or have other things you spend money on that you don't really need, maybe you could cut back on one of those things & be able to afford to buy organic. You only get one body in your lifetime. Treat it with care. It'll last longer.