Thank you for your query,
It is very difficult to associate a skin condition to the giving formula milk without the physical examination of the skin rash
Was the child fuusy or irritable?
Any loose motions or colic
or vomitings aftere the formula started?
Any family history of food allergy?
Thes are important to comment and consult your Pediatrician
for the examination of the rash and advise you properly.
Hope I have answered your query.