Before anyone can accurately help ya on this on, we're going to need more information. What lights are you using? temps? humidity? soil? watering schedule?
If your using fluorescent you can usually let them touch with no problems, my plants routinely grew up into my fluorescents, and never burnt. If your using CFL's (compact fluorescent) then keep them at least 2 inchs away depending on air circulation.. i kept my cfls 5 - 6 inchs away.
my first guess would be overwatering though:jointsmile:
:weedpoke:
:twocents: