My wife was just at a grocery store and a checkout girl told her that calamine lotion (zinc oxide + ferric oxide) had been correlated to kidney failure. My wife was going to get it for my daughter who has some mosquito bites and this checkout girl's statement caused her to get some far more expensive clay stuff instead.
This just sounded absolutely absurd to me, so I thought I'd ask about it here.
In my searching, I can't find any references elsewhere to calamine (or caladryl, its other name) and kidney failure. About the only thing I can turn up is a connection between cadmium and kidney failure, such as this quote from Medicine Plus, a service of the US National Library of Medicine:
Note that many zinc products also contain another metal called cadmium. This is because zinc and cadmium are chemically similar and often occur together in nature. Exposure to high levels of cadmium over a long time can lead to kidney failure. The concentration of cadmium in zinc-containing supplements can vary as much as 37-fold. Look for zinc-gluconate products. Zinc gluconate consistently contains the lowest cadmium levels.
Calamine, however, is zinc oxide, not pure zinc. It's not clear whether or not zinc oxide containing products suffer from the same potential risk of cadmium contamination as those containing pure zinc.
Is there any evidence that calamine lotion (aka caladryl) contains anything that might be positively correlated with kidney failure from moderate topical use?
It's hard to qualify "moderate"... I have used it less than 10 times in my entire life. The most was for chicken pox and perhaps some bug bites when I was a kid.
Let's cap usage as topical application to the skin in approximately 2.5cm diameter blots applied to 10 spots on the body for three consecutive days and doing this once per month. Doing an insanely rough calculation, if the application coating thickness is 0.5mm (pretty darn thick, in my opinion), this would be (pi x 2.5cm^2 x 0.05cm) x 10 spots x 3 consecutive days x 12 months = 141.3 cm^3 / 141.3 mL / year applied topically.