It is really not uncommon for some eye products to cause swelling if applied at night.
Some eye products are specifically designed to be used in the day under your moisturiser. I cannot say whether or not this is the case with your particular eye product? It really does depend on what the product has been designed for. It could very well be that you have a sensitivity to an ingredient. It may also be, as you’ve said, a contact dermatitis, but the likelihood would then be that all products that contain the active to which you are reacting, would cause dermatitis where it’s used.
So if you are using other products from the range, I would compare the ingredient lists of the various products and see if they all contain Methylisothiazolinone. It is a preservative, so it is quite possible that this preservative is used across all the products in the range, and if it were that you are reacting to is… you would most likely develop the contact dermatitis wherever it is used.
