The present invention aims to elucidate the relationship between fulvic acid contained in a humic substance and the onset mechanism of the type I allergy, and inhibits the onset of the type I allergy using the fulvic acid. The present invention provides a type I allergy inhibitor which inhibits an antigen sensitization phase or/and an antibody sensitization phase, and the degranulation phase of cells with fulvic acid and a composition containing at least the fulvic acid. Moreover, the present invention provides a method for inhibiting the onset of the type I allergy by performing a specific hyposensitization treatment using the fulvic acid and, in particularly, a method for inhibiting an antigen sensitization phase or/and an antibody sensitization phase with fulvic acid. Or, the present invention provides a method for inhibiting the onset of the type I allergy by performing a nonspecific hyposensitization treatment using fulvic acid.