Recent studies have shown that the pH of exhaled breath condensate (EBC) could be predictive of asthma exacerbation. Moreover, it has been documented that both allergic rhinitis and atopic dermatitis constitute risk factors for the occurrence of asthma in a progression of disease known as atopic march. The aim of our study was to establish if condensate pH could be used as a valuable mean of monitoring of asthma in atopic children. We studied 34 atopic children with acute asthma, 70 with stable asthma, 35 children with allergic rhinitis, and 17 with atopic dermatitis. Thirty healthy children were used as controls. All children underwent skin prick tests and lung function tests. Exhaled breath condensate samples were collected with a condensing device and de-aerated with argon. The pH of EBC was measured using a pH meter. Children with acute asthma were treated with inhaled steroids and bronchodilators. We found that the pH of condensate in patients with acute asthma was lower than that of patients with stable asthma, rhinitis, and controls (7.25 vs. 7.32, p < 0.05; 7.25 vs. 7.48, p < 0.02; 7.25 vs. 7.78, p < 0.0001, respectively). Patients with stable asthma, rhinitis, and eczema had also lower pH than that of controls (7.32, 7.48, and 7.44 vs. 7.78; p < 0.0001, p < 0.006, p < 0.04, respectively). Patients with acute asthma normalized their pH after treatment (7.82 vs. 7.25; p < 0.0001). Finally, patients with acute asthma showed a positive correlation between pH and lung functional parameters (forced expiratory volume in 1 s; r = 0.39, p = 0.04). Our study shows that EBC pH measurement may be a promising marker for assessing airway inflammation and monitoring response to anti-inflammatory treatment in asthmatic children. Furthermore, we report the first evidence of airways acidification in children with allergic rhinitis and atopic dermatitis. Therefore, EBC pH assessment may be useful in the evaluation of progression of the atopic march toward the development of asthma later in life. Further studies are recommended in order to confirm this indication.