Well, there have not been any studies showing that MSM causes toxicity or toxic buildup. And MSM may be one of the safer nutritional supplements. Take too much, of course, and you might regret it. According to the Mayo Clinic, you might feel nauseous, have a headache or suffer from diarrhea.
They key is to make sure that you are getting the highest quality MSM, because it can vary so much. The lower the quality of MSM, the more trouble you will have.
First of all, think about your nose. Some products that contain sulfur, which is what makes rotten eggs so odiferous, have been known to cause some rather malodorous side effects. Typically, MSM supplements avoid this problem, but you have to make sure the MSM product you buy does not have other sulfur compounds that do induce and olfactory assault on the proboscis.
There are other problems to think about. Like allergies.
MSM is found naturally in foods like milk and pine nuts. Researchers have speculated that those with certain allergies to certain foods cannot take MSM as a supplement. While true of other supplements, like glucosamine, verboten to those who suffer food allergies, that is not the case for MSM, which is produced synthetically.
However, some manufacturers may combine MSM with other compounds, so before taking any MSM, look for any allergens on the label.
But even more importantly, make sure your MSM is high quality. Some low-rent supplements have minute amounts of lead, mercury or other heavy metals, which can build up in your system. And, if your MSM is made where they make other synthetics, it may be contaminated, say with benzene or, sometimes, even pesticides.
How can you avoid a bad batch?
Make sure your MSM has been purified by distillation, not crystallization, which can cause toxins to accumulate.