its all about the halogens in your environment. flourine in stain resistant this and that and water and toothpaste and powdered eggs and god knows there its hidden, like in teflon non-stick pans and stuff. then there is bromine which is in so many materials in our lives as a fire retardant. https://www.nationalgeographic.com/science/article/chemicals-within-us notice the date.
big cities and public trans and buildings are the worst. i have had my face go numb just walking into a lazy boy outlet due to flame retardants and stain treatments, etc. no idea how people do 8 hours a day in that. this was in austin and i was taking 700mg a day to keep all that at bay.