What are phthalates and do they cause asthma?

There has been much interest in the role of phthalates in the development of many different diseases including reproductive and developmental problems, but what are they? Phthalates are a class of chemical that is used in manufacturing processes to make products (usually plastics) softer or more pliable and can be found in numerous every day products including cosmetics, children’s toys, shower curtains and even food. Now new research suggests that perhaps phthalate exposure during pregnancy may increase the risk of developing asthma, raising the question, does phthalate exposure cause asthma? The simple answer is no. The complex answer? Well read on to understand.

Asthma is classified as a complex disease, meaning it doesn’t have one cause (unlike cystic fibrosis that is caused by a defect in one gene). Complex disorders may be the result of many different genetic changes and environmental exposures that together interact to lead to the development of a disease (in this case asthma). As such, there is no one thing that can cause someone to get asthma and there may be multiple roots of exposure that can lead to someone developing asthma or any other complex diseases.

In this recent study by Whyatt and associates, it was shown that exposure to two types of phthalates during pregnancy (BzBP and DBP) was associated with having children who had a greater risk of developing asthma or asthma like symptoms at some point in their life (to be precise 70% more likely). They came to this result by measuring the amount of phthalates in the urine of the mother at one point during their third trimester and then following the children for years to determine if they eventually developed asthma. It should be noted that this increase in asthma risk was only seen for the highest levels of phthalate exposure and not for the lower end of exposure.

These results are interesting as they link an environmental exposure to the development of asthma, but they should be taken with a grain of salt until they are replicated by other studies. This is because of two things,

  1. The people in this study had high rates of maternal and childhood asthma. This means this population is already at a high risk for asthma and therefore these results may just indicate the role of phthalates in triggering the development of asthma in people who are already at risk for or have asthma.
  2. The population of people in the study only had the levels of phthalates measured once in their urine and could therefore be wrongly classified as being exposed to high levels or low levels of phthalates (meaning the association with asthma could be wrong).

Still, it provides an intriguing story that has been developing about home phthalate exposure during pregnancy and childhood disease. Other research has shown that the presence of phthalates in the house is associated with a child having asthma, however another study showed that just because children has more phthalates in their urine doesn’t mean they were more likely to develop asthma. This likely indicates that exposure to phthalates during pregnancy is important for the development of asthma.

The study, although interesting, needs to be validated in a larger group of people from various genetic and geographical backgrounds before we can definitively say whether phthalates are one of the factors important in contributing to asthma. This could be done by a recent study going on called the “Canadian Healthy Infant Longitudinal Development study” or CHILD study. They are measuring almost every variable imaginable in parents houses (like phthalates, dust, dander, nutrition, animals, stress and more) and trying to see which of them relate to the development of asthma, allergy or eczema in the children of these mothers down the road. The results of this study will be exciting and go a long way to helping us understand how asthma and allergic diseases develop.

If you are starting to worry about phthalates here are a couple quick facts and resources to help educate yourself:

Should we be worried about phthalates? The research so far suggests that exposure to phthalates during pregnancy may contribute to the risk of developing asthma but is not alone responsible for asthma. People must also have a genetic susceptibility as well as exposure to other environmental triggers. It is more likely, at this moment, that the children in this study are primed to develop asthma (because of their genes) and that the phthalates act to push them over the edge towards asthma. There is plenty of research to show that pollution and diesel exhaust or viral infections early in life may trigger asthma in those who are susceptible to the disease. So it is unlikely that phthalates are the cause of asthma alone. Instead, all these triggers act to make a susceptible person develop asthma.

Still you can try to reduce your exposure to them but you do not (nor can you) need to remove them completely. It is not exposure to phthalates that is the problem but rather the amount you are exposed to. If you lick a soft plastic toy you will be fine, however if you lick that toy every hour like a child would, that is the problem. More research still needs to be done before we blame phthalates on the rise in asthma.

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