Nere's what I've collected and compiled from this list. Accuracy is unknown.
Hope it help you find the hidden culprit.

Milk Related Ingredients:
Acidophilus milk
Butter
Buttermilk
Calcium Caseinate
Calcium lactate
Caramel *
Casein - milk protein
Caseinate
Cheese
Coffee whiteners *
Condensed milk
Cottage cheese
Cream
Cultured milk
Curds
Custard
Dried Milk
Evaporated milk
Ghee
Hydrolysed milk proteins
Hydrolized Vegetable Protein (may contain whey) *
Ice cream
Lactalbunin - milk protein
Lactoglobulin - milk protein
Lactate
Lactose
Malted Milk
Margarines, most *
Milk Solids
Mayonnaise, some, mostly diet ones *
Natural flavors *
Non-dairy creamer *
Potassium Caseinate
Pudding
Seasonings *
Sherbet
Sodium Caseinate - milk Protein *
Sour cream
Whey =’s milk protein & milk Sugar *
Whey Powder
Yogurt
Yogurt powder

* Ones with * may be dairy or not, please call the manufacturer to be sure.
 Above From:    [log in to unmask] (Laurie Carson) [log in to unmask]
and From:       [log in to unmask] (Hazel and Ray Green)  By: Hazel Green - Feb. 4/97

Calcium lactate is the calcium salt of lactic acid, with is a carbohydrate.
It is not a milk product. I once called the Minute-Maid company, the brand of
calcium-fortified OJ we use (frozen concentrate), and they assured me it was
a fruit-based source.  Also, there is a kosher symbol (the K in a triangle)
with no D, DE or M after it, so it is Parve.  (From individuals on no-milk
list)

This is from http://www.kashrus.org/kosher/chem.html:
Calcium Sterol Lactylate Source: milk or soybeans. Use: instant mashed
potatoes. Requires kosher supervision.

Calcium Stearoyl Lactylate
Source: chemical reaction of stearic acid and lactic acid. Use: as a dough
conditioner, whipping agent and as a conditioner in dehydrated potatoes.
Requires kosher supervision

Caramel Color
The problem with caramel color is it may or may not contain gluten depending
on how it is manufactured.  In the U.S.A. caramel color must conform with the
FDA standard of identity from 21CFR CH.1.  This statute says- The color
additive caramel is the dark-brown liquid or solid material resulting from
the carefully controlled heat treatment of the following food-  grade
carbohydrates:
        Dextrose (corn sugar)
        Invert sugar
        Lactose (milk sugar)
        Malt syrup (usually from barley malt)
        Molasses (from cane)
        Starch Hydrolysates and fractions thereof (can include wheat)
        Sucrose (cane or beet)
  (Also acids, alkalis and salts are listed which may be employed to assist
  caramelization) - Excepts from Ener-G Food's "Detailed Ingredients
Listing":

Casein
Casein is an excellent glue. White glue, used in woodworking and sold as
Elmer's Glue-All, is pure casein. Note it is sold by Borden and has a cow on
the front.

Lactic Acid
· Sources: molasses, corn starch, glucose, molasses. Use: preservative,
flavoring. (Lactic acid can also be produced from whey, in which case it is
dairy, but its use is restricted to ice cream and cream cheese). Kosher,
Pareve without supervision.
· Lactic acid is a colorless, syrupy liquid formed in milk, sauerkraut, and
some pickles from the fermentation of sugars.  It is also a by product of
muscle metabolism formed by the breakdown of glycogen. (Glycogen is the term
for glucose that is stored in the muscles and liver).
· This is not true. Lactose is not destroyed, it is broken down into glucose
and galactose by lactase, an enzyme in the gut (usually insufficient or
totally lacking by age 3 or 4. Lactic acid is not stored in muscles, it is a
byproduct of anaerobic muscle activity. Lactic acid has nothing to do with
lactose intolerance. By Daniel A. Twogood, D.C.

Lactylate  I have seen it on products marked with a parve hechsher.  Is it
dairy or not?
It can come from both dairy and non-dairy sources.  If it's in a product with
a reliable parve hechsher you can probably safely assume that it's from a
non-dairy source, but depending upon the severity of your son's reactions you
may wish to call the company to confirm that.  I've been told that sodium
stearoyl lactylate is a fat-based ingredient that is not normally made from
milk, but I don't have a source to back that up.

Stearyl Lactylic Acid
Source: fats and oils. Use: emulsifier. Requires Kosher supervision. (Kosher
forms are often dairy.)

Stearic Acid
Source: animal or vegetable oil. Use: in butter and vanilla flavoring,
softener in chewing gum.  Requires Kosher supervision.

FOODS TO WATCH
Water packed ham can have dairy in the ham without being on label. In 1992
the USDA's Food Safety and Inspection Service approved the use of milk and
soy derivatives as binders in these hams.  The ingredients are listed on the
label, per FAN's Off to School with Food Allergies book

Natural Flavors can be dairy too.

KELLOGG'S ready-to-eat cereal products which are milk/whey free include
All-Bran, All-Bran Extra Fiber, Apple Cinnamon
Squares, Blueberry Squares, Bran Buds, Common Sense Oat Bran Flakes,
Complete Bran Flakes, Corn Flakes, Corn Pops, Crispix, Healthy Choice
Multi-Grain Flakes, Healthy Choice Multi-Grain Squares, Just Right with
Fruit & Nuts, Mueslix Raisin & Almond Crunch with Dates, Nutri-Grain
Almond Raisin, Nutri-Grain Golden Wheat, Nutri-Grain Golden Wheat &
Raisins, Product 19, Raisin Bran, Raisin Squares, Rice Krispies, Smacks,
and Strawberry Squares.

MAPLE: The one item I am surprised isn't on that list of strange places to
look
is in maple syrup (real or flavored).  Whey is usually added to real
100% maple syrup to stop the foaming action during boiling it down, and
then the scum is scooped off, but some protein will always remain.
Hungry Jack brand is pareveunlike most other store brands and very few
100% brands are.  It seems strange not to be able to buy 100% maple
syrup, but I haven't found one yet that can guarantee no whey was used
or was marked pareve.


Sodium Benzoate My nephew, who is very lactose intolerant, is also _very_
sensitive to sodium benzoate, as well as a number of artificial colors used
in foods. After he was diagnosed as LI and his diet became dairy-free, most -
but not
ALL - of his symptoms disappeared. This was troubling until the sodium
benzoate problem was diagnosed, and since then he has been virtually
trouble-free. I don't know if this is a possibility for you, but I do know
that his reaction to the sodium benz was, as you described, symptoms similar
to, but not quite as severe as, his reaction to dairy. When I read that, and
saw the sodium benz in your mayo, it rang a bell. For what it's worth...

NOT MILK:
Glucono delta lactone is a variation of glucose and is manufactured from
corn starch.  I will spare you the biochemistry.  It is added to the food
probably to aid in formulation, as it is an acidifier.  It is not a milk
product.