ACTIVE VS. INACTIVE INGREDIENTS

Any foray into clean skin care and better skin health starts with getting more familiar with the ingredients we put on our faces every day. However, reading the ingredient label, known as the International Nomenclature Cosmetic Ingredient (INCI) list, can quickly feel like trying to understand a foreign language.  Furthermore, because active ingredients are potent, expensive, and used in many different chemical formats, they can be difficult to recognize at the bottom of the INCI list. But what about all of the ingredients at the top? And what makes an ingredient active or inactive? 

ACTIVE INGREDIENTS: PRODUCT INTENT

According to the FDA, an active ingredient is defined as “any component of a drug product intended to furnish pharmacological activity or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease, or to affect the structure or any function of the body of humans or other animals” [1]. While this definition is framed in the context of disease-targeted therapeutics (which over-the-counter skin care is not), this can be boiled down to say active ingredients are those that accomplish the intended effect as advertised on the label. 

INACTIVE INGREDIENTS: PRODUCT CHARACTERISTICS

Inactive ingredients may serve any of the following purposes for a product [2]:

• Texture modifiers (e.g. binding agents, fillers, surfactants)
• Active stabilizers (e.g. buffers and molecules that prevent separation of hydrophilic/-phobic ingredients)
• Preservatives (e.g. antimicrobials, antioxidants, or enzymes that slow active breakdown)
• Pharmacokinetic modifiers that alter absorption and metabolism of active ingredient
• Aesthetic additions (e.g. scent and color)

EXAMPLES: MOISTURIZERS AND VITAMIN C

Based on the list above, it’s clear thatinactive ingredients are just asessential to the final product as the active ingredient(s). In fact, depending upon the intent, inactive ingredients can act as active ingredients. Many of the active ingredients in moisturizers are considered inactive in other products that are specifically targeted towards a certain goal or condition.For example, glycerin is almost never considered the active ingredient although it functions as a humectant and is widely present in moisturizing skin care products [3]. 

Lastly, we want to bring attention to the fact that many actives are often chemically modified to increase bioavailability and stability. These modifications may disguise the INCI name of the active even further in the ingredient list. A common example is vitamin C which is actually not very stable or skin permeable in its base form, L-ascorbic Acid [4]. Instead, more effective formulations use Ascorbyl-6-Palmitate, Tetrahexyldecyl Ascorbate (THD), or Magnesium Ascorbyl Phosphate (MAP). Since this ingredient is present at concentrations of 1-10%, it may be near the middle or bottom of the list compared to ingredients like water, squalene, and carrier oils since the list is ordered from highest to lowest presence in the overall formula.

TAKEAWAY

Although not considered actives, many of the inactive ingredients affect how a product feels, is delivered to, and penetrates the skin barrier. They are just as vital to the effectiveness of the product and are generally inert, safe, and less expensive “support” molecules that optimize the function of the active ingredient(s).

Sources:

[1] Research C for DE and (2022) Inactive Ingredients in Approved Drug Products Search: Frequently Asked Questions.FDA.

[2] Pottel J, Armstrong D, Zou L, Fekete A, Huang X-P, Torosyan H, Bednarczyk D, Whitebread S, Bhhatarai B, Liang G, Jin H, Ghaemi SN, Slocum S, Lukacs KV, Irwin JJ, Berg EL, Giacomini KM, Roth BL, Shoichet BK, Urban L (2020) The activities of drug inactive ingredients on biological targets.Science 369, 403–413.

[3] Becker LC, Bergfeld WF, Belsito DV, Hill RA, Klaassen CD, Liebler DC, Marks JG, Shank RC, Slaga TJ, Snyder PW, Gill LJ, Heldreth B (2019) Safety Assessment of Glycerin as Used in Cosmetics.Int J Toxicol 38, 6S-22S.

[4] Al-Niaimi F, Chiang NYZ (2017) Topical Vitamin C and the Skin: Mechanisms of Action and Clinical Applications.J Clin Aesthet Dermatol 10, 14–17.