Lactose is dairy according to the OU but not according to Reb Elyashiv
The FDA and Halacha define “dairy” differently.
According FDA regulations only something consisting of actual milk in certain forms can be labeled dairy. Milk derivatives or milk by-products may not, according to FDA, be called dairy. Many of these so-called creamers use a lactose that is a derivative from milk.
According to Halacha, a derivative of milk is still milk, and must be labeled dairy accordingly. According to the FDA, such a product may not be labeled dairy because that would be lying to the consumer (remember, they say only milk is dairy) To comply with FDA regulations, the company must label the product as a NON-DAIRY creamer. To comply with Halacha, this product must have a dairy designation.
I think it would appropriate to mention HaRav Elyashiv's position in this matter see. Rabbi MGR
All foods derived from or containing milk are considered dairy, or milchig (Yiddish). I think it would appropriate to mention HaRav Elyashiv's position in this matter see. This includes milk, butter, yogurt and all cheese – hard, soft and cream. Even a small amount of dairy in a food can cause the food to be considered dairy. All dairy products require kashrut certification. They must meet the following criteria in order to be certified kosher:
They must come from a kosher animal.
All ingredients must be kosher and free of meat derivatives. Non-kosher dairy products are often made with ingredients of animal origin. For example, hard cheese is made with rennet, yogurt sometimes contains gelatin, and butter may contain non-kosher additives.
They must be processed on kosher equipment.
Many kinds of “non-dairy” creamers, candy, cereal and margarine do contain milk derivatives, as do some low-calorie sweeteners. Dairy ingredients whose names appear on many product labels include caseinate, lactose and whey.
Commercial bread containing dairy ingredients presents kashrut problems. Consult an Orthodox Rabbi before purchasing or using any dairy bread.