diff --git a/IPython/core/shellapp.py b/IPython/core/shellapp.py
index d9ca71d..b1aae11 100644
--- a/IPython/core/shellapp.py
+++ b/IPython/core/shellapp.py
@@ -176,8 +176,11 @@ class InteractiveShellApp(Configurable):
         """
     )
     pylab_import_all = Bool(True, config=True,
-        help="""If true, an 'import *' is done from numpy and pylab,
-        when using pylab"""
+        help="""If true, IPython will populate the user namespace with numpy, pylab, etc.
+        and an 'import *' is done from numpy and pylab, when using pylab mode.
+        
+        When False, pylab mode should not import any names into the user namespace.
+        """
     )
     shell = Instance('IPython.core.interactiveshell.InteractiveShellABC')