Human Repeat Insult Patch Testing with 50 people showed that 2% East Cape mānuka oil has good skin compatibility and does not cause any sensitising effects (Eurofins Romania 2021).

A recent review article makes the following observations (Matthew et al., 2020):

• Gel formulations containing >10% mānuka oil (did not induce acute skin sensitivity in mice).
• The irritation potential of 10% mānuka oil was tested on the chorioallantoic membrane of chicken egg and using the Eyetex and Skintex assays. All three tests deemed the product to be non-irritant, non-comedogenic and well tolerated on skin.
• The product safety report on b-triketone rich mānuka Oil (<5%) according to EC Regulation 1223/2009 detailed high skin tolerance and good cosmetic acceptance. There was no skin sensitization. No irritation was noted on testing the formulation on rabbit eye mucous membranes.

Toxicity

Mānuka Oil (<5%) did not demonstrate genetic toxicity after a micronucleus test in TK6 Human lymphoblastoid cells and bacterial reverse mutation test in Salmonella typhimurium and Escherichia coli. Acute toxicities were LD₅₀ = 1061 mg/kg body weight and LD₅₀ > 2000 mg/kg body weight for oral and dermal administration, respectively.

Reference: Matthew, C. et al., (2020) Mānuka Oil – A Review of Antimicrobial and Other Medicinal Properties, Pharmaceuticals 2020, 13, 343; doi:10.3390/ph13110343, published online 26 October 2020.