The term hypoallergenic is used in marketing primarily for cosmetics. There is a misconception to what the term actually means compared to its perceived definition.

For the consumer when they hear this term they believe that it will not cause an adverse allergic reaction. For those who have sensitive skin this may be a term they look for when shopping for non irritating skincare. 

The problem is that this is not a guarantee. The definition of hypoallergenic is that it is "relatively unlikely to cause an allergic reaction." What the manufacturer is trying to say when they use this term is to make the consumer aware that the product was formulated with ingredients that causes fewer allergic reactions. 

It would be extremely hard to make products that are 100% allergy free. Our body chemistry changes especially as we age and go through hormonal imbalances. What once was non-allergen may now be.

At the end of the day, this term is more of a marketing term. If yo have sensitive skin be sure to read the ingredients listing to make sure you are not allergic to any of the ingredients listed regardless is they are "relatively unlikely" to cause an adverse reaction.