Preservatives allow formulas to remain fresh during the long span between the time of manufacture and the time the customer finishes using it. There are strong and powerful preservatives (e.g. formaldehyde-releasing preservatives and parabens) that essentially permit the product to be used almost indefinitely and allow for significantly increased shelf life.
Why It’s Commonly Used: Elongate freshness
Why We’ll Seriously Never Use It: Irritant, carcinogen, toxicity