There are many causes of glans erythema, including physiological factors, drug allergies, and pathological factors such as glans vulgaris, early changes of a tumor, syphilis, psoriasis, and lichen planus. Physiological factors are commonly caused by frequent sexual intercourse, or washing the foreskin and glans with soap or shower gel, which are irritating cleansers. There is also a possibility that the foreskin is too long and the coronal sulcus of the foreskin and glans harbors a lot of dirt that irritates the glans causing redness. Some drug allergies can also cause a fixed red rash that can appear on the glans. When certain patients are allergic to drugs, the glans is a good site for this rash, which is often a round or round-like dark red spot, and in severe cases, it can blister or even ulcerate, and it tends to recur. Pathological factors are common in glansitis caused by various pathogenic microorganisms, such as Escherichia coli, Enterococcus, Candida, Mycoplasma or Chlamydia, Trichomonas, etc. These can be cured with targeted treatment. The proliferative erythema caused by carcinoma in situ of penile cancer needs timely consultation at regular hospitals; malignant lesions of glans penis in early stage such as eczema-like cancer, the erythema will be bright red and swollen. If infected with syphilis, red spots can appear on the glans, mostly in the second stage of syphilis, with some scales on the surface. There are also conditions that can cause red spots on the glans, such as psoriasis and flat moss on the glans, etc. The red spots caused by psoriasis will have flaking on the surface, and the red spots caused by flat moss are dark purple-red. So once the glans red spot appears, go to the hospital as soon as possible to do a checkup, clear the cause, early treatment, so as not to delay the disease.