This is a big one as often allergies are actual sensitivities to either something they are eating, or something in their environment.
Skin and coat issues, eye, ear, intestinal and others can often be helped with a change to a clean diet.
Dr Sergio at Forza has made it a life passion with over 30 years of research into why pets are having so many health issues. You can read more about that here
A couple of the formulas you should note if you are reading this that are very specific are
Forza10 Dermo - for itchiness on back, base of tail, neck and sometimes paws
this is a result of sensitivity to the food (possibly oxytetracycline)
switching to a clean food could resolve
Forza Immuno - for itchiness on belly/chest and sometimes paws
this is a sensitivity to the environment - eg seasonal allergies (if the sensitivity is to something not natural like a cleaning product, this formula will probably not help)
consider this a "reset" for the immune system
All the foods on this site have the ability to combat inflammatory issues that pets are struggling with, so I have chosen to not list them all here.
Just remember, think clean protein with no antibiotics, no GMO's (nor ingredients fed GMO ingredients), high digestibility and stay clear of commodity purchased ingredients as often it is what the ingredients eat, not the ingredient itself that is causing the problem.
You are not only what you eat, but also what you eat eats...or is sprayed with...or if it's modified genetically...
PLUS - Check for the proper balance of Omega 6 to Omega 3
Omega 6's are inflammatory- a good thing to a certain extent as inflammation works to combat bad things in the body by expelling them. Problem is too many leads to too much inflammation (chronic). Omega 6's are very common
Omega 3's are anti inflammatory to help keep them in check.
Ideal ratio should be around 4:1 to 1:1 (or less) (Omega 6:3)
Remember - The effects of inflammation can look a lot like allergies so your pet may not be allergic to as much as you thought!