Brief Answer:
Zinc oxide based cream will help

Detailed Answer:

Hi,

The most common cause of rashes on bum in this age is diaper rash. Other less common cause is allergy or infection.
Skin lesions are better identified by direct examination.
I request you to attach an image if possible so that I better able to help you out.

For diaper rashes application of zinc oxide based cream like Rashfree, Happynap etc., helps in early healing.
Change the diaper immediately after soiling and keep the area open in air to make it dry. While cleaning avoid rubbing rather use wet wipes for gentle cleaning. You can apply the cream four to five times a day. If the condition is not improving or processing rapidly please consult your pediatrician.

I hope this helps.
Please let me know if you have any more questions.
Wishing for your baby's good health.
Regards

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