Icing consists almost entirely of sugar, so it should not be included as part of a Paleo lifestyle. The sugar is mixed with some sort of liquid (such as water, milk, or cream) so it can be spread on top of baked goods.
Of course, you shouldn’t be eating anything you would put icing on anyway, but maybe you want to make some Paleo cupcakes. Can you put icing on them? What if we make the icing with more milk and cream than sugar?
Milk is also pretty high in sugar, so you won’t be doing yourself any favors by adding it to sugar. Even cream doesn’t have enough fat to counteract the sugar rush icing will give you, so you’re better off avoiding it altogether.
The Dangers of Sugar
Studies have shown sugar inhibits the immune system, increases cortisol (the hormone your body makes when under stress), decreases appetite, increases insulin resistance (leading to diabetes and heart disease), and may even promote cancer (source). So icing is definitely off the Paleo menu.