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, if controlled, is not a contraindication for dancing. Whether it has got any positive effect on asthma course or symptoms has not been proven in randomised controlled studies. Some Indian studies have proven pranayam to be beneficial to asthmatics.
There is a special variant of asthma called exercise induced asthma, where any sort of exercise, even dancing too may lead to asthma attack. The mechanism is, increased airflow through airways lead to cooling effect and drying of airways causing degranulation of cells which causes airway constriction and asthma attack.
If one has got this particular type of asthma, then better take your reliever inhaler before going for dance.