Are there side effects to using Vitamin B12?

The vitamin B12, or cobalamin, is a water-soluble vitamin that is essential for the body. It is synthesised exclusively by certain bacteria, and its intake in humans is achieved via diet or through dietary supplements. The vitamin B12 can also be found in cosmetic formulations under the INCI name "Cyanocobalamin". When applied to the skin, this molecule is highly valued for its anti-inflammatory and regenerative properties, as well as for the rosy colouration it imparts to cosmetics. Suitable for pregnant women, the vitamin B12 can alleviate skin irritations and the characteristic itching of certain dermatoses.

When applied topically, vitamin B12 is an active ingredient that is generally very well tolerated.

Nevertheless, there are a few rare cases of reactions to vitamin B12 reported in scientific literature. These side effects are minor and primarily manifest as temporary rednessThis can be explained by the sensitivity to cobalt that some individuals exhibit. Cobalt is indeed a relatively common allergen, with the prevalence of susceptibility in the overall population estimated at about 5% by a study in 2014. If vitamin B12 triggers a similar reaction, it is because a cobalt core is found in its chemical structure. The cessation of the application of the vitamin B12-based skincare product results in the end of the reaction.

Regarding the oral intake of vitamin B12, the trend is slightly different. Several cases ofacne outbreaks have been reported in the literature following the oral intake of this molecule, which can be explained by the dependence of the anaerobic metabolism of Cutibacterium acneson vitamin B12, the bacteria involved in acne. Studies in vitro have indeed shown that supplementing vitamin B12 in cultures of C. acnes promotes the synthesis of porphyrins, molecules that induce inflammation in acne.

Furthermore, an overdose of vitamin B12 can contribute to the occurrence of pigmentation problems such as hyperpigmentation or vitiligo. In the body, this vitamin plays a role in the regulation of melanogenesis. Therefore, some studies have shown that a deficiency or, on the contrary, an excessive intake of vitamin B12, can lead to pigmentation disorders.

Good to know : It is estimated that a typical diet provides between 3 and 30 μg/day of vitamin B12, which amply covers the estimated needs of between 2 and 10 μg/day in adults.

The cosmetic use of vitamin B12 very rarely leads to allergic reactions. However, if you have a sensitivity to cobalt, it is wise to exercise caution before applying a skincare product containing vitamin B12. Generally, to prevent risks, it is recommended to test your cosmetics on a small part of the body during the first use. The recommended areas for this are the crook of the elbow or the wrist, often used during dermatological patch tests as they are considered representative. After applying the cosmetic to be tested, it is advised to wait 24 to 48 hours to observe any potential redness, swelling or irritation. Of course, in the event of immediate discomfort, the product should be rinsed off without delay.

• SAMMAN S. & al. Vitamin B12 in Health and Disease. Nutrients (2010).

• SCHNUCH A. & al. Contact sensitisation to cobalt--multifactorial analysis of risk factors based on long-term data from the Information Network of Departments of Dermatology. Contact Dermatitis (2014).

• DAVLUY S. & al. A Review of Vitamin B12 in Dermatology. American Journal of Clinical Dermatology (2015).

• BARBARESCHI M. & al. Acneiform eruptions caused by vitamin B12: A report of five cases and review of the literature. Journal of Cosmetic Dermatology (2018).