As nutritional supplements go, MSM seems to be one of the safer ones out there. No studies have established any toxicity or toxic buildup [source: MSM Guide]. If you take too much MSM, you may experience a bit of diarrhea, nausea or headache [source: Mayo Clinic]. But that's probably it. However, there may be other side effects depending on the quality and production of your MSM supplements.
Sulfur is what makes rotten eggs smell so bad, and some sulfur-based supplements have been known to have particularly stinky side effects. MSM typically doesn't do this, but you should make sure your supplement doesn't contain other sulfur compounds [source: The Arthritis and Glucosamine Information Center].
MSM occurs naturally in several foods, such as pine nuts and milk, which has led to speculation that people with some food allergies can't take MSM supplements [source: MSM Guide]. Although there are nutritional supplements (such as glucosamine) that are off-limits to certain food allergy patients, that's not the case for MSM. All MSM in supplements is synthetically produced [source: MSM Guide].
However, that doesn't mean you're home free on the allergy front. Different manufacturers may combine MSM with different ingredients. Before taking MSM, you do need to check these ingredients for allergens or other chemicals that might be contraindicated with your current prescriptions.
Even more importantly, be aware that the quality of synthetic MSM can differ dramatically. Some inferior MSM supplements contain trace amounts of heavy metals, such as lead and mercury, and those most certainly can build up in your system, with toxic effects. If it's produced at plants that produce other synthetic chemicals, some MSM may contain other contaminants, such as benzene or -- depending on the manufacturer -- pesticides [source: Bergstrom Nutrition].
How do you steer clear of such dangers? Look for MSM that has been purified by distillation, not crystallization. The crystallization process is where toxic elements can accumulate. Distilled MSM, on the other hand, ought to be chemically identical to the naturally occurring molecules [source: MSM Guide].
What if you're hoping to use MSM to build up something non-toxic -- say, hair or muscle? Read on.