A top U.S. health official told lawmakers Tuesday that e-cigarette market leader Juul uses salts in its vaping devices that she said could be particularly dangerous for teenagers.

“Juul products use nicotine salts, which can lead to much more available nicotine,” CDC Principal Deputy Director Dr. Anne Schuchat told the House Oversight and Reform Committee’s panel on consumer products. She said doctors believe the salts allow nicotine to “cross the blood brain barrier and lead to potentially more effect on the developing brain in adolescents.”