This study was designed to determine whether a unique cellulose powder extract could prevent the classic hay fever attack from occurring among volunteers who have suffered for some years. Nasaleze enhances nasal mucus, which allows the filtration of allergens, to ensure that only clean air reaches the lungs. One hundred two volunteers were recruited and, using a simple 5-point scoring system to grade their general well-being and severity of any hay fever attacks, the overall average score was 3.85, indicating that Nasaleze was able to control hay fever very well. Rapid relief of symptoms was also demonstrated, sometimes within minutes after inhalation. Overall, 77% of volunteers reported a significant reduction in the number of challenges throughout the study period and most graded Nasaleze as more effective and reported fewer side effects than with a wide range of chemical treatments.