Wow, when I was taking medical statistics, the key example of a confounding variable was the correlation between Sunscreen use and skin cancer. According to medical statistics, the correlation between sunscreen and cancer was the epitome of correlation does not equal causation. However, my Dermatology professor in med school actually warned us against using high SPF sunscreen. Sun screen back in the day, used to be inorganic Zinc and Titanium. These white metal salts reflect UV and visible sun rays, but because they are ionic, they are not absorbed into the skin. However, most sunscreen today is white but instead of zinc and titanium, today's sunscreens contain a mixture of organic molecules which are slowly absorbed by the skin. So, while they do reflect sun light what actually happens is that many of these substances become activated by the sun, transforming into toxic free radicals, where they then absorb deeper into the skin and into cells and damage DNA even more than UV light ever could. Therefore, my Dermatology professor told us that when we use sunscreen it should be a low SPF and washes off easily and would need to be reapplied.
Kudzu is a pesky non-native vine that grows all over Atlanta, GA and many other cities in the Southeast United states. This plant has been affectionately named, "the plant that ate Atlanta." New studies have shown that this plant actually produces high levels of ozone which is terrible for asthma. This is interesting because asthma seemed much worse in Atlanta than Augusta having worked in both and Augusta has very little kudzu.