Background: User-independent quantitative measures of cutaneous allergic reactions can help the physicians manage and evaluate the treatment of cutaneous allergic reactions. In this paper, we present and validate a method to quantify the elevation, volume and area of cutaneous allergic reactions to red tattoos. Methods: The skin surface of allergic tattoo reactions was imaged using an optical 3D scanner. The in-house developed analysis tool measured the elevation, volume and area of the lesions, compared to a reference surface. This reference surface was created by 3D interpolation of the skin after manual removal of the lesions. The error of the interpolation tool was validated using a digital arm model. The error of our optical scanner was determined using a 3D printed lesion phantom. The clinical feasibility of the method was tested in 83 lesions in 17 patients. Results: The method showed clear potential to assess skin elevation, volume change and area of an allergic reaction. The validation measurements revealed that the error due to interpolation increases for larger interpolation areas and largely determined the error in the clinical measurements. Lesions with a width ≥4 mm and an elevation ≥0.4 mm could be measured with an error below 26%. Patient measurements showed that lesions up to 600 mm2 could be measured accurately, and elevation and volume changes could be assessed at follow-up. Conclusion: Quantification of cutaneous allergic reactions to red tattoos using 3D optical scanning is feasible and may objectify skin elevation and improve management of the allergic reaction.