Store bought dressing will last two to three months after opening if properly stored. The acidic vinegar based versions last longer than ones containing dairy. How To Store Homemade Italian Dressing Homemade Italian Dressing Recipe Kristine's Kitchen How Long Does Opened Salad Dressing Last In The Fridge? Italian dressing is a staple in our kitchen at Pietro's Trattoria. You have probably used it countless times in your own kitchen. It's great to use on salads; some people even use House Blend Italian Dressing Fanny Mencoboni's