My 14 Year Old Son Got In A Hot Tub

My 14 year old son got in a hot tub at a friends house and when he came home his shorts that were worn in tub smelled very strong of mildew. The following day he began coughing and cough is getting worse and keeping him up at night. Had a history of cough variant asthma when he was younger. I feel like his symptoms are directly associated with exposure to mold/mildew in hot tub. I am very concerned about how I need to treat symptoms and if there will be any long term effects from this? I have albuterol and a nebulizer. I also have a diffuser with 100% pure essential oils. I like going the natural route first. I have always made a conscious effort to not use chemicals in our home (make my own cleaners) so I am mortified over his exposure. Washed shorts worn in hot tub twice - cannot get mildew smell out. Says he was in for about 30 minutes - outside (cold) - lots of steam coming up in his face. Can this exposure have perminent affects? I'm sorry - I can't afford to have my question answered - wasn't aware of fees.