When the weather is hot, a small red patch like a rash appears on the child's face. When the weather is not hot, it disappears. What's going on?

The condition you are talking about should be prickly heat, also known as "hot prickly heat" and "red milia". It is caused by excessive sweating in a hot and muggy environment, and the sweat evaporates poorly, causing the sweat ducts to be blocked. , caused by rupture of sweat ducts and sweat leakage into surrounding tissues. The main symptoms are small papules and small blisters, which tend to occur in summer and are more common in children with poor perspiration regulation function and long-term bedridden patients.

This condition can be treated with topical talcum powder and, if necessary, calamine lotion.