Evaluation of the irritation and sensitization potential of medical-grade Norway spruce (Picea abies) resin salve: single-blind modified draize human repeat insult patch test in healthy volunteers.

Background: Abilar^® is a wound salve containing 10% medical-grade Norway spruce (Picea abies) resin, known for its antimicrobial and wound-healing properties. However, isolated reports of allergic contact dermatitis have raised concerns regarding its cutaneous safety profile. It is thus important to evaluate any potential for skin irritation and sensitisation.

Objectives: To evaluate the irritation and sensitisation potential of the resin salve using a modified Draize Human Repeat Insult Patch Test (HRIPT) in a healthy adult cohort, thereby providing toxicological insights relevant to both clinical applications and consumer safety.

Methods: A single-blind study was conducted with 215 healthy volunteers (207 completed the study). The resin salve was applied through cutaneous patches in an induction phase and a challenge phase. Skin reactions were evaluated using modified Draize scoring system.

Results: During the induction phase, only 7 of 207 subjects (3.38%) of participants exhibited mild erythema (Grade 1) attributed to the resin salve. Notably, no participant experienced moderate to severe reactions (Grades 2-5). In the subsequent challenge phase, no reactions were observed, and subjects with prior Grade 1 responses reverted to a non-reactive status.

Conclusions: The HRIPT findings demonstrate that medical-grade Picea abies resin salve has a low irritation and sensitisation potential under the conditions tested. Although rare allergic contact dermatitis cases have been reported, the data of this study suggests that the overall risk in the general population is low. These findings are also supported by clinical studies and extensive post-market surveillance of Abilar^® in wound care for both acute and chronic wounds.