Sexually transmitted infections may involve the anus and cause rectal itching. Pinworms can cause persistent rectal itching. Other parasites could cause similar itching. Yeast-based infections, which often affect women, can also cause itching in the rectal area. Skin conditions. Sometimes rectal itching is the result of a specific skin condition, such as psoriasis or contact dermatitis.
Thrush and fungal infections are caused by germs that thrive in moist, warm, airless areas, such as across the anus.
Just as a condom containing spermicidal lubricant can provide a woman a yeast infection, anal sex on a man can give him an anal yeast infection.
How Do You Get Rid Of Your Itchy Anus?
If you already have anal itching, try these self-care measures:Cleanse smoothly. After bowel movements, clean the region with plain drinking water or mild soap. Dry thoroughly. Don’t scratch. Wear cotton underwear and loose clothing. Avoid irritants. Apply ointments or gels. Maintain regular, solid bowel movements. 
Just How Do They Diagnose Pinworms?
Diagnosis is made by identifying the worm or its eggs. Worms can sometimes be seen on the skin near to the anus or on underclothing, pajamas, or sheets about 2-3 3 hours after drifting off to sleep. Pinworm eggs can be collected and examined using the “tape test” as soon as the individual wakes up. 
What Pinworms Look Like?
In stools, the worms look like small bits of white cotton thread. For their size and white color, pinworms are difficult to see. The male worm is rarely seen since it remains inside the intestine. It is best to search for pinworms during the night, when the feminine comes out to lay her eggs.