First you have to search for the email address of the company, it has to be the customer service department.
Second, you have to give as much as many questions about the product that you would like to inquire about, examples are "is this good for my skin type? (dry moisturized," Is this hypo allergenic and all those stuffs.
3rd, you have to let them know how could they reach you back to discuss your inquiry, a work email maybe or a phone number, who knows? Some good company calls their clientele to respond on inquiries.
Lastly, keep a copy of the email on your inbox to make sure that if ever you would have to resend it again you wont have to make a novel again.