Asthma is caused by inflammation of the small tubes, called bronchi, which carry air in and out of the lungs. If you have asthma, the bronchi will be inflamed and more sensitive than normal.
When you come into contact with something that irritates your lungs – known as a trigger – your airways become narrow, the muscles around them tighten, and there is an increase in the production of sticky mucus (phlegm).
Common asthma triggers include:
•house dust mites
•animal fur
•pollen
•cigarette smoke
•exercise
•viral infections
Your son may have different triggers than the ones above, everyone is different. The cold or the air being very dry can also trigger of an asthmatic cough.
You can get Vick that is suitable for children, and you can apply that to your son's chest and back. You can buy plug ins that emit vapours to help to loosen up congestion. You can also place a bowl of hot water with some Vick in it in his bedroom - making sure that he not get at it. The steamy menthol vapours will help with decongesting the tubes.
Milk encourages the formation of mucus. As it is important for him to have his milk for healthy teeth and bones, perhaps only give him a watery drink before bed time rather than a milk drink. Viral and bacterial problems can cause formation of mucus and coughing is the body's way to get rid of the irritant.
Have you tried using the inhalers?
Perhaps it would be a good idea to get the mucus analysed by the laboratory to find out if this is caused by a viral or bacterial infection. Ask your doctor if this can be done.
Make sure you give your son plenty of warm drinks and soups. Chicken soup is very good.
For me this all doesn't make sense. Asthma is allergic, so how is it possible, he doesn't show any allergies. Since when is he diagnosed with autism? Try to get a different opinion from someone, who is experienced with autism plus physical pediatric problems.