Background:  Oral challenge is widely used for diagnosing food allergy but variable interpretation of subjective symptoms may cause error. Facial thermography was evaluated as a novel, objective and sensitive indicator of challenge outcome.

Methods:  A total of 24 children with a history of egg allergy underwent oral challenge, which were scored positive when objective symptoms occurred or negative after all doses were consumed without reaction. Facial temperatures were recorded at baseline and 10‐min intervals. The difference between mean and baseline temperature (ΔT), maximum ΔT during challenge (ΔT_max) and area under curve of ΔT against time (ΔTAUC) were calculated for predefined nasal, oral and forehead areas, and related to objective challenge outcome.

Results:  There were 13 positive and 11 negative challenges. Median nasal ΔTAUC and ΔT_max were greater in positive compared with negative challenges (231‐ and 5‐fold, respectively; P < 0.05). In positive challenges, nasal temperatures showed an early transient rise at 20 min, preceding objective symptoms at median 67 min. There was a sustained temperature increase from 60 min, which was reduced by antihistamines. A cut‐off for nasal ΔT_max of 0.8°C occurring within 20 min of the start of the challenge predicted outcome with 91% sensitivity (positive predictive value [PPV] 100%) and 100% specificity (negative predictive value [NPV] 93%). Subjective symptoms occurred in four of 13 positive and three of 11 negative challenges.

Conclusions:  Facial thermography consistently detects a significant early rise in nasal temperature during positive compared with negative food challenges, which is evident before objective symptoms occur. Thermography may therefore provide a sensitive method to determine outcome of food challenges and investigate the pathophysiology of food allergic reactions.