Itch in the scrotum area and around anus, from time to time there apears red plate like rash around anus. What could this be?

Candida. A yeast infection is one possibility. Another is inflammation from hemorrhoids, anal fissure or proctitis. A trial of micatin (miconazole) may help. If symptoms are persistent sigmoidoscopy to check for anal problems is advised.
Most often due to. Caffeine and excess moisture. Mayt turn into a yeast infection. If caught early corn starch powder liberally to the are works well. If this doesn't clear, see a dermatologist or better a colorectal surgeon. Biopsy may be necessary.