Complex sentence: Some products containing SLES have been found to also contain low (up to 279 ppm) levels of 1,4-dioxane, with the recommendation from the U.S. Food and Drug Administration that these levels be monitored.
Split into simpler sentences: Some products containing SLES have been found to also contain traces (up to 279 ppm) of 1,4-dioxane. The U.S. Food and Drug Administration recommends that these levels be monitored.