When using firming body lotions and moisturizers, potential side effects may include skin irritation, redness, or allergic reactions, especially if you have sensitive skin or are allergic to any of the ingredients. It is important to check the ingredient list for any known allergens and do a patch test before using the product all over your body. Additionally, some firming body lotions may contain ingredients that could interact with certain medications or skin conditions, so it is recommended to consult with a dermatologist or healthcare provider if you have any concerns.