Redness in the coronal sulcus may be due to a certain inflammatory reaction in the area. Inflammation in this area is usually caused by fungal infections, resulting in local flushing. Especially after yeast infection, large diffuse erythematous patches may appear in the area or in the area around it, as well as in the foreskin area. Some patients may have a certain amount of scaling on top of the erythema, and in severe cases there may be a certain amount of exudative reaction. This redness may also be due to the patient’s allergy to some condom substance or condom material after sexual intercourse, resulting in irritant dermatitis. Of course, it cannot be ruled out that the infection is syphilis, so it can cause a painless red inflammation in the area.