Hi -
If sodium stearoyl lactyate is *sometimes* milk derived, but it is
found in a kosher meat or kosher pareve food, then that particular form
of it is NOT milk derived. The laws of kashrut would prohibit it. If
it is NOT in a kosher meat/pareve food, then people with low tolerance
for milk should certainly phone the manufacturer before trying it.
That's my take on the issue.
--Beth Kevles
[log in to unmask]http://web.mit.edu/kevles/www/nomilk.html -- a page for the milk-allergic