Car Technology

A few years back I attended a conference of the American Student Medical Association and was shocked to learn that on a hot day, there are chemicals that can come out of certain plastics that you might say try their darndest to make everyone (men and women) more womanly.  You might think I’m joking, but I’m not.

One of the sessions at the conference which left a lasting impact on me was presented by two epidemiologists (a man and a woman).  The puzzle these two doctors had chosen to try to solve was why the average of girls developing breasts was changing over time. It wasn’t changing a little, it was changing a lot.. I remember that when I was in 6th grade, about half the girls in my class had noticeably started to develop breasts. I was shocked to learn in the epidemiologists’ presentation that if I were in grade school now, I would be observing the same thing in third grade. ”Third Grade?!” I couldn’t believe it. But apparently this was really happening, and had been happening for a while, and there was a theory that the cause was a class of chemicals called phthalates.

Phthalates are used (among other things) to make vinyl (technically PVC – Poly Vinyl Chloride), which is hard and brittle in its pure form (like and old vinyl record or a PVC drain pipe) more soft and flexible, so it can be used for applications like upholstery covering, flooring, and shower curtains. The epidemiologists explained that when phthalates enter the body, they get into the bloodstream and act as estrogen precursors, signaling the body to produce more estrogen.  Estrogen has the effect of making both men and women “more womanly”.

When vinyl gets heated up (for instance, by the sun shining on it), some of the phthalates come out and become airborne, and people can inhale them. As children inhale them, it changes the balance of estrogen in their bodies, causing girls to grow breasts earlier. For years, doctors had been concerned about this and had been requesting regulations on the auto industry to reduce the use of vinyl in car interiors. Congress ignored these requests, until a correlated effect on men’s sperm count was found.

The epidemiologists showed a slide which include two graphs, side-by-side. The graph on the left was the average age of onset of puberty (age at which girls start noticeably growing breasts) of girls in the US, versus the calendar year.   The age was about 12 throughout history until 35 years ago or so, when it started decreasing. The decreasing was steep for a while and then the curve showed signs of leveling off at an asymptote. The projected asymptote (if no changes were made in society’s use of vinyl) would be that in the future the average girls would start developing breasts at age 6 or 7.

The study that showed the decreasing age at which girls were developing breasts had not convinced congress to act. The second graph had. The second graph showed sperm density of the average 30-year-old man in the United States, versus the calendar year. That graph had also been flat until about 35 years ago, when it started to ramp down. It continued to ramp down through 1997, almost perfectly linearly, with no signs of an asymptote. If that graph had been projected 15 years into the future, half the 30-year-old men in the United States would be sterile.

While congress had decided it didn’t mind if all the 9-year-old girls had boobs, it certainly minded if half the men in the country became sterile, so some regulations got passed, and slowly the use of vinyl in car interiors has decreased, but there are still plenty of vinyl floors, and plenty of vinyl shower curtains.   So if you are a man and you buy a new vinyl shower curtain and you notice that “new vinyl smell”, beware, your shower curtain is actually creating estrogen in your body and turning you into a girly man.  Likewise, if you notice a hazy thin oily film inside your car windshield after some hot summer days, that’s most likely dioctyl phthalate, an estrogen precursor.

So what can you do in the modern world to maintain your reproductive health and keep from turning into a girly-man? If you have a car with vinyl seats or dashboard, when you are going to get into the car on a hot day, open the doors for a minute and let the vaporized phthalates escape before you climb in and breathe them. Don’t buy vinyl shower curtains, buy the woven polypropylene ones (they cost a little more, but they have that added advantage that they can be washed in a washing machine). And lastly, don’t buy vinyl flooring or vinyl-upholstered home furniture, unless you can verify that it has been made without phthalates.