On the 2nd of March Danielle King asked me about MS, that I suspect is a short name for multiple sclerosis and reactions to bay leaf in her diet. I am no medical doctor as I already told her, but I like browsing through the available information to know more and help others know more about their own conditions. Having said that, if you're ever concerned about your health or the health of any of your relatives, especially in such serious intricate ailments like MS, it is always very important to rush to your doctor and get an appropriate follow-up of your symptoms with professional medical advice.
Defining Multiple Sclerosis?
To start with let's define what is Multiple Sclerosis; the National Health Service (NHS) website explains it as a disease in the brain and spinal cord that will ultimately affect muscular movement, affect sight (loss of vision) and cause ataxia (affecting coordination and balance) and cause spasticity and tiredness . There are different types of patients suffering from MS, 8 out of 10 with MS will show the relapsing remitting type where symptoms are milder or can periodically disappear but the relapse events can flare-up and last for weeks to months. Later on in life, half of the people suffering from MS develop secondary progressive MS where symptoms gradually become worse and remission periods become rarer. There is a less common type of MS disorder known as Primary Progressive MS where symptoms gradually get worse and there are no periods of remission .
If you want to know more about causes, patients and outlook, please visit this link.
What did I find on the available scientific literature about Bay leaf and Multiple Sclerosis?
Unfortunately not much, if anyone has access to better articles or better servers where articles are located, please by all means, just let me know. I found some studies on anti-alcohol substances from natural resources explaining that bay leaf (Laurus nobilis) showed very strong inhibitory activity on ethanol absorption in rats . This same article by Yoshikawa et al. talks about a few pharmacological properties of bay leaf. Focusing solely on the leaves one can learn about the inhibitory effects on NO production (I suspect NO stands for nitrogen monoxide) and also anti-diabetic effects, for example.
In another article Yalcin et al tell us about the different compounds found in the essential oil of Laurus nobilis from the Northern Cyprus mountains . If we look into a few of them and cross along with the information on pharmacological properties of these, maybe we can deduct something important. Bear in mind that a deduction is merely a deduction and not a clinical trial at all!!! Thus, verifying the different compounds composing this oil monoterpenes and sesquiterpenes form a bigger part of the constituents:
- it is reported by David Stewart, PhD, R.A, that monoterpenes are capable of reprogramming miswritten information in the cellular memory ; sesquiterpene molecules deliver oxygen to cells just like haemoglobin in blood, thus creating an oxygenated moiety that inhibits the growth of cancer cells, and are also capable of erasing or deprogramming miswritten codes in DNA.
But what caught my attention was Dr. Stewart's comment that I fully transcribe hereby:
"The American Medical Association (AMA) has said that if they could find an agent that would pass the blood-brain barrier, they would be able to find cures for ailments such as Lou Gehrig's disease, multiple sclerosis, Alzheimer's disease, and Parkinson's disease. Such agents already exist and have been available since Biblical times. The agents, of course, are essential oils-particularly those containing the brain oxygenating molecules of sesquiterpenes."
In other articles I found online regarding atherosclerosis (very different from multiple sclerosis for the former is a form of obstruction of arteries by 'fatty' atheromas/plaques, a combination of turmeric and bay leaf is associated to reduced plaque build  in a hypercholesterolemic Zebrafish model, and blood sugar levels  in patients with diabetes Mellitus (very limited study though).
I honestly believe that maybe what you feel is an allergic reaction to bay leaves as face eczema, contact dermatitis and occupational asthma have been reported before .
I don't want to conclude anything at all, but to provide information for you to do your own interpretation. A GP might be able to indicate better why you have face flushes and feel sick after having your bowl of soup with bay leaves in it. From the top of my head, unless you are using a copious amount of leaves in your soup, inadvisable though, I see no direct link between the information I was able to find and your complaints, unless we focus on side-effects. These, related to consumption of bay leaves, are overall very few when consumed in food.
 NHS Choices, Multiple slerosis, [http://www.nhs.uk/conditions/multiple-sclerosis/Pages/Introduction.aspx], last visited on the 19th of March 2014, last update on the 18th of March 2013.
 Yoshikawa, M., Shimoda, H., Uemura, T., Morikawa, T., Kawahara, Y., Matsuda, H. (2000). "Absorption inhibitors from bay leaf (Laurus Nobilis): structure requirements sesquiterpenes for the activity". Bioorganic and medicinal chemistry, 8, pp. 2071-2077.
 "Yalcin, H., Anik, M., Sanda, M. A., Cakir, A. (2007). "Gas chromatography/Mass spectrometry analysis of Laurus nobilis essential oil composition of Northern Cyprus". Journal of medicinal food, 10(4), pp.715-719
 The blood-brain barrier, [http://www.rnoel.50megs.com/pdf/theblood.htm], last visited on the 19th of March 2014, last update unknown.
 Jin, S., Hong, J-H., Jung, S-H., Cho, K-H. (2011). "Turmeric and Laurel Aqueous extracts exhibit in vitro anti- atherosclerotic activity and in vivo hypolipidemic effects in a Zebrafish model". Journal of Medicinal Food, 14(3), pp. 247-256.
 Aljamal, A. (2011). "Effects of bay leaves on the patientswith Diabetes Mellitus". Research Journal of Medicinal Plant, 5(4), pp. 471-476.
 Healthline, Bay leaf (Laurus Nobilis), [http://www.healthline.com/natstandardcontent/bay-leaf], last visited on the 19th of March, last update unknown.
1st image taken from Irish American Mom, Bay leaf and thyme sprigs in soup, [http://www.irishamericanmom.com/2012/02/06/potato-and-leek-soup/dscf7537/], last visited on the 19th of March 2014.
2nd image taken from Circulation research, [http://circres.ahajournals.org/content/104/8/952/F1.expansion.html] on the 19th of March 2014.