What Causes Severe Itching On My Upper Back?

sir my problem is that i will severe itching on my body specially the upper back when i do some vigorous physical work such as dance or play and also when i get anxious i will heat throughout my back.Also when there is a bit warm atmosphere around me i feel the same.Few days back i put some cool talcum powder on my back and then rubbed it,then i felt somewhat relieved.Please suggest what to do.