Alimentum is milk-based and may not be sufficiently broken down to avoid triggering a milk allergy. If I were you, I'd switch your son to a completely dairy-free formula for a few weeks to see if the eczema clears up. Eczema can be a delayed-type reaction to foods (including milk), so it may take a while for it to clear once he is on a milk-free diet.
Check out http://nomilk.com/ for more info on milk allergy.
Gluten & Sulfite Sensitivity, Multiple Food & Inhalant & Medication Allergies, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD (Lupus?), Osteoporosis, Anemia, Very Low Lymphocyte Counts (T-Cells & B-Cells), malabsorption/malnutrition, etc.
Meds: Pulmicort, Injectable Vitamin B12, Herbs, Nutritional Supplements, Essential Oils, Homeopathy.