Are synthetic preservatives dangerous?

Cosmetics require preservation to guarantee protection against potencially pathogenic microorganisms and against biological and physicochemical deterioration.
The most common strategy is based on the application of antimicrobial agents (preservatives), synthetic, natural, or both.
Successful preservation depends on several factors. In regulatory terms, a preservative is a substance of natural or synthetic origin intended to inhibit the development of microorganisms . This inhibition should be effective over different types of micororganisms and should have a duration longer than the cosmetic product itself.
Overall, an ideal preservative should be stable, compatible, effective at low levels, non-toxic, consistent with cosmetic legislation, and non-expensive.
The efficacy of the preservative system and the minimum required dosage for a natural preservative system in a product must be determined by microbial challenge tests and stability tests.
Choosing whether to use natural or synthetic preservatives for cosmetics is an important decision that has many implications. It will affect product stability, odor, appearance, texture and most importantly, cost.
Whilst natural preservatives might not offer the degree of preservation sought, chemical preservatives have been shown to have consequences for the health and well-being of people and society when used in high doses and over long periods. In addition, the same substance can be found in more than one product and can derive from different sources (“additive effect”). Some undesirable effects for consumers, which can appear either after first contact or after years of cosmetic use range from mild irritation of the skin to estrogenic activity and, in the latest, it can be related with the mammary tumors.
So coming back to the title question, are synthetic preservative dangerous? Not all of them are dangerous but we must certainly avoid some that have been proven to be dangerous for our health, for example Parabens and Formaldehyde.
Sometimes, using the right packaging (for instance coloured dark glass) allow us to have natural preservatives in our products instead of chemical ones. In other occasions, like in clay masks, a natural preservative is not enough to stop microorganisms from spreading and a chemical preservative must be used.
From Bllue Tansy Skincare, our advice is to always double check the list of ingredients in your products and avoid those likely to produce skin reactions (parfumes, parabens, high quantities of alcohol...). Try to choose natural products when possible but bear on mind, sometimes, when safety or performance is at stake, a chemical compound could be used as last resource.
Halla N, Fernandes IP, Heleno SA, et al. Cosmetics Preservation: A Review on Present Strategies.Molecules. 2018;23(7):1571. Published 2018 Jun 28. doi:10.3390/molecules23071571
Panico A, Serio F, Bagordo F, et al. Skin safety and health prevention: an overview of chemicals in cosmetic products.J Prev Med Hyg. 2019;60(1):E50‐E57. Published 2019 Mar 29. doi:10.15167/2421-4248/jpmh2019.60.1.1080