Some highly hydrolysed milk formulas are suitable for babies with cows’
milk allergy, but other types of
formula, such as partially hydrolysed
milk and soya formulas, aren’t suitable, because many babies with cows’ milk allergy might react to them as well.
http://www.theallergysite.co.uk/dairy.html
You can get blood tests like RAST or skin ***** test done to find whether your child will be allergic to soy milk or not.That is the only way of confirming the allergic reaction.