The main causes of redness and pain in the foreskin of the reproductive organs are foreskin allergy, glans and sexually transmitted diseases. 1. Foreskin allergy: If the foreskin on the genital organ comes into contact with allergens like animal dander, mites and so on, so that the foreskin produces an allergic reaction, under the stimulation of histamine and other immune factors, the blood vessels of the foreskin dilate and the nerves contract, and the redness and pain of the foreskin can appear. 2. Glans inflammation: If bacteria, fungi and amoeba infect the glans, the genital foreskin can be red and painful under the double stimulation of inflammatory factors and pathogenic microorganisms. 3. Sexually transmitted diseases (STDs): If the genitourinary organs are infected by pathogens such as human papilloma virus, syphilis spirochete and Neisseria gonorrhoeae because of unclean sexual behavior, and STDs are triggered, these pathogens can stimulate the genital foreskin to become red and painful. If the genital foreskin is red and painful, there may be other reasons, it is recommended to actively seek medical treatment under the guidance of a professional physician.