You're right to check to make sure she's thoroughly wiped, since this is one of the most common causes of anal itching in young children, especially those who are just learning to use the potty. Other things to look for include:
- Reaction to Detergents
- Yeast Infections
- Irritation caused by spicy foods or citrus (especially orange juice)
Since you stated that much of her itching occurs at night and keeps her awake, a pinworm infestation is likely the cause. More information about formal diagnosis and treatment for pinworms is available here. In addition, if you suspect a yeast infection, contact your physician for treatment options.
Other issues can be treated at home as follows:
- If your child consumes a lot of spicy foods or citrus fruit or juices, try eliminating them from the diet for a couple of weeks and see if the situation improves.
- Try using dye-free, perfume-free soap on your child's undergarments. Make sure you aren't using fabric softener, which can also cause irritation to these senstive areas. If you use scented toilet paper or wipes, try the plain varieties without scents or dyes, as well.
- Apply Witch Hazel with a cotton ball or pad. You can find this liquid at most drug and discount stores. It is very mild and soothing. (This is one of the main ingredients in Tucks pads).
- Prepare a special bath and let your child soak for 15 minutes or so twice daily. You can mix about 1/4 cup baking soda in a tub of warm water or you can use a colloidal oatmeal bath such as this one made right at home.
- After those baths, make sure the area is completely dry. Moisture provides the ideal environment for yeast growth, which can cause further irritation. To promote dryness, you can also use cornstarch on the area and be sure to change underwear frequently, especially on hot days or during potty training when even small leaks can cause enough moisture to be a problem.
- Make sure the area stays clean. Those new to potty training may need some help for a while until they get the hang of wiping properly (front to back) and thoroughly. Invest in some flushable wipes if your child has those hard-to-wipe BMs.
- If all else fails, there are a variety of anti-itch creams (usually containing hydrocortisone) that can safely be used in the area. These are for external use only and you should first consult with your physician about proper usage and dosing, especially in children under two years of age. (Your doctor may be able to prescribe a special low-dose cream in this instance.)
In addition, make sure that your child's fingernails are trimmed so that he will not injure himself when scratching, and clean them daily with a soft nail brush and antibacterial soap.