Certain ingredients used in dermatological formulations are known to result in skin irritation and allergy. For instance, preservatives have often been reported to cause allergic contact dermatitis. Parabens are commonly used as preservatives in foods, drugs and cosmetics.1

A study evaluated the effects of the daily use of methyl paraben (MP) on human skin. Researchers measured the concentrations of MP in the stratum corneum (SC) of the human forearm after daily applications of MP containing formulations. The effects of long-term exposure to MP on keratinocytes were also studied in vitro. Following 1 month of daily application of MP containing formulations, MP remained unmetabolized and persisted slightly in the SC. MP was found to reduce the proliferating ability of keratinocytes and changed the cell morphology. MP also decreased the expressions of hyaluronan synthase 1 and 2 mRNAs and type IV collagen. It was shown to increase the expressions of involucrin and HSP27. MP exposure thus leads to MP persistence and accumulation in the SC, and seems to affect the aging and differentiation of keratinocytes.1

Additionally, there is much controversy regarding the possible endocrine-disrupting effects of parabens. Studies have shown parabens to have a weak estrogenic activity. They have been suggested to cause disruption of hormones of male fetuses and young children and have been reported to have adverse effects on fertility. Furthermore, parabens have also been linked with breast cancer.2 Research has reported the detection of unconjugated parabens in breast cancer tissue.3 Parabens inhibit 17β-hydroxysteroid dehydrogenase (17β-HSD2).3 They have been found to inhibit sulfotransferases (SULTs) in human epidermal keratinocytes and skin cytosolic fractions. As a result, they block local estrogen conjugation and inactivation. Chronic application together with a potential accumulation of parabens in the skin has been suggested to increase local estrogen concentrations due to the inhibition of SULTs.3 Subcutaneous accumulation of parabens as a result of extensive use of dermally applied products is accountable for the endocrine disruption due to the interference with estrogen sulfation by parabens.3 Parabens can penetrate into the human circulatory system after a single topical cosmetic application.4

Considering the controversies surrounding the use of parabens, it only seems wise to use paraben-free formulations.

References

1. Ishiwatari S, Suzuki T, Hitomi T, et al. Effects of methyl paraben on skin keratinocytes. J Appl Toxicol. 2007 Jan-Feb;27(1):1-9.
2. Garner N, Siol A, Eilks I. Parabens as preservatives in personal care products. Available from: https://www.researchgate.net/publication/262068680_Parabens_as_preservatives_in_personal_care_products.
3. Engeli RT, Rohrer SR, Vuorinen A, et al. Interference of Paraben Compounds with Estrogen Metabolism by Inhibition of 17β-Hydroxysteroid Dehydrogenases. Int J Mol Sci. 2017;18:2007.
4. Darbre PD, Harvey PW. Paraben esters: review of recent studies of endocrine toxicity, absorption, esterase and human exposure, and discussion of potential human health risks. J. Appl Toxicol. 2008. Available from: https://theorganicpharmacy.com/Images/Content/ExpertAdvice/FactSheets/Files/107.pdf.