Can we ask job applicants about their allergies?

Q. In a hiring interview, is it lawful to ask a candidate if they have a particular allergy to something that they will come into direct contact with on a daily basis and could be life-threatening to them? Specifically allergies to nuts/peanuts in a private daycare situation. We've discovered that with some folks exposure to even the smell of peanuts or peanut butter is life-threatening to them, even when they have an EpiPen with them at all times. -- Anonymous, Virginia