Greetings: I don't know per say what this could be, and since you are dealing with Autism, there may be no telling what is the cause, but I have a problem myself with violent behavior. I know what causes mine, but do not know why. I do not know if any of these might be affecting your son, but you might look into it.
A recent study has just tied VOC's in cleaning products in the home to the massive increase in children's asthma in this country. It was on our local news stations about six months ago. I don't have the classical allergic reactions to these things like itching, burning, rash, hives, or breathing difficulties. Instead I can experience violent outbursts under the following circumstances:
An half-hour or more of exposure to chemicals or products which give off Volatile Organic Compounds (VOC's) including:
Most Perfumes and Colognes, including those in soaps, hair care products, and laundry detergents, fabric softeners, and anti-static dryer sheets.
Cleaning Products (Except chlorine bleach, alcohol, and ammonia)
Air Fresheners, Potpourri, scented candles (synthetic scent only, most natural oils or scents don't bother me, except oil of wintergreen,which gives me a blinding headache from the smell)
Oil or Petroluem-based paints and solvents
Laquer
Varnishes and oil-base stains (polyurethanes, etc.)
Acrylic resins
Acetone
Paint Thinner and Laquer Thinner
Cigarette smoke
Epoxy
Car Exhaust
Petrochemicals
Brake Part Cleaner
Contact Cement, rubber cement, and other such adhesives
New Synthetic Carpet
New Vinyl or PVC sheeting
Some Plastics
Dry-erase or Permanent markers
Pesticides
Herbicides
And the list goes on. Essentially, for me, if it has a smell and it isn't organic (plant related, like fruit, flowers, etc.) Synthetics are the worst. I cannot be around it for more than a few minutes before coming down with headache, fuzzy vision, dizziness, disorientation, and soon after, red vision and angry, violent behavior. It takes me 6 or more hours to come down off a bad exposure. Because these things affect my mind first, sometimes I don't realize it is happening to me until it is too late. Usually I have just enough shreds of civilization left to realize I need to get away from people until I come down.
Acetominophen will cause this to happen in me almost the moment I take it. The last (only the second time I ever took any) time I ingested acetominophen it took 3 people to get a baseball bat out of my hands.
I was 13, 5'4" and weighed about 115 lbs at the time. I have met only one other person who told me that
Tylenol (And he said it through gritted teeth) made him "Really, Really Tense!" I am in the process of researching this problem right now, to see if I can find out why.
Wheat allergy is also known to cause violence in children, usually the kids who are reacting to this have big black circles under their eyes when it is happening to them. Used to affect people who worked in flour mills, was called millers syndrome or millers disease, I think.
Some friends of mine had a hyper kid they took off tunafish and his behavior improved dramatically. We don't know why.
None of these is what would be considered a standard "allergic" reaction. Allergy tests may or may not reveal some of these kind of symptoms.
Is the kid on any mood-altering drugs? Anything that elevates his serotonin levels? I am currently pursuing this as a possible clue to my own problem, having found a reference to this as a rare side effect of acetominophen. Serotonin Syndrome can cause agitated behavior or mood swings. There are a number of drugs which can produce it, especially in combinations.
Does he experience the violent behavior within say two to three hours of having eaten a meal? Low blood sugar causes irritability and mood swings. Very severe hypoglycemics can run around naked, self mutilate, and become temporarily sociopathic and not even know they are doing it. I get it to a much lesser degree. In my case, if I get hungry enough, the irritability factor skyrockets, and I feel so bad physically that I will go through whoever is standing in front of me in order to get to the food just to try to feel better and not even care what I have just done until the sugar levels start to come back up. Sometimes I may remember what I did or said, but not always. As long as I remember to eat about every 3-4 hours, this is not a problem.
Consequently, I have never taken alcohol or drugs, and when my doctor prescribes medicine for me that I have not taken before, he gets a sample and I take it and sit in his office for several hours until we see what it is going to do to me. It has been 9 years since my last one of these episodes was induced by a 3 hour exposure to an epoxy compound in my Wood class in college. It has taken me many years to recognize the progression of the symptoms so I can remember to get away from the smell before it goes too far.
Again, I don't know if any of this will help you, but it can't hurt to look. I wish you luck in your search.
Autism Aggression 
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