My 7-week-old baby has a red pimply rash on her face and neck for the past week. It started out on the face, cheeks mainly, and now it is on the neck too. It does not cause any discomfort as far as I can tell. Any ideas as to what causes this? Is it heat or milk? I live in a cold climate. And is there anything I can do to treat it or should I leave it alone?
There are many possible causes. At that age, it can't hurt to talk to your pediatrician. Obviously cortisone creams and other typical anti-rash agents aren't always a good idea for newborns (or babies younger than three). Based on the health of your baby, environment, diet, et cetera, different treatments may be more or less effective (and safe).
If it's only been a day or so, I wouldn't worry much about it. If it lasts longer than 2-3 days, or if it seems to be painful or itchy or otherwise bothering your baby, I'd point you to the pediatrician again. :)
No one can diagnose your baby over the internet, especially when no details are given (is the baby sick? Do you live in a hot climate? How long has the rash been there? Is it spreading? Does it seem to be causing any discomfort? Etc., etc.) There are many questions to ask, and a physical exam to perform, to answer this kind of query.
Rashes in newborns are quite common, maybe the most common being acne neonatorum (newborn acne, caused by mother's high hormone levels transferred to newborn in utero) and *Milia/miliaria * (plugged up sweat and sebaceous glands that appear as pale little bumps on the nose, etc.) Those are usually present at or shortly after birth. Common red rashes appearing later are heat rash, diaper rash and others. I've not heard of rashes attributable to milk (breast? Formula? Spilling onto baby's skin?) in babies of this age.
Heat rash looks like this:
Kind of scary looking to me, but very common. It should respond to decreasing sweating: lighter, dry, breathable clothing, decreased contact against bare skin (if that's how you feed him) and plastic if it's warm where you are, etc.
Dr. Sears (who I greatly admire) discusses other common rashes in children on his website.
The first question always to ask yourself is, does the baby seem to be at all sick? This could mean crying more than usual, waking frequently at night, being off feeding, being feverish, acting irritable, having a runny nose/coughing/anything that would cause a parent concern. If the answer is yes, take him to the doctor. That is always the safest bet, and that is what the doctor is there for.
In the meantime, reading the Dr. Sears page and the references (with pictures) might help.