Try SWAT ointment-a Farnum product available at most feed & tack suppliers. It has a texture much like zinc oxide, so sticks on pretty well. And contains insect repellant plus ingredients to promote healing. I use it down the mid-line of my horses' tummies, under the jaw, in the ears-wherever they develop those chewed-up spots from gnats & flies. One application seems to last 3-4 days on my horses. It comes in clear or hot pink, which at first I thought was ghastly. But now I can see an advantage to the pink in that it is easy to see at a glance when the horse needs more. Just not the best if you are showing! It was developed as a wound ointment, so no worries about applying it to raw areas.

     Also, just a warning about the Skin-So-Soft-although it can work well, esp. to repell gnats, some horses react badly to it. My niece's horse missed the whole count fair because of an allergic reaction to this product. The vet clinic where I work is generally called out 2-3 times a summer to give antihistimines to horses after Skin-So-Soft use. 

  

My Morgan mare was really affected by the "noseeums" and she had rubber her beautiful long mane out, rubbed all the hair off her whole underside and was starting on the top of her tail.  She wore a fly sheet, sprays, and connoctions on her belly.  I tried everything I could think of for about 4 years. It only lasted during late spring, all summer and early fall but it was devastating.  I was even thinking I might have to consider putting her down ( a thought I couldn't even imagine) due to her misery.  A friend told me about an immune builder and I tried it and it worked!  I have used the immune product from Blueridge Botanicals www.bluerb.com and my horse does not itch anymore at all.  She was on an immune builder for about a year and only during for those months when they bother her.  She is now not on anything except their Wintreats and a supplement. Her mane has grown out, her hair on her belly hair is back and she looks beautiful. Best of all she is not on the ground trying to scratch her belly all the time!  Believe me when I say I tried everything!

It seems like everyone has good ideas. My mare is alos very sensitive to bugs. I'm glad I'm not alone. Her belly itches so much that she begs me to rub and scratch it continually. This weekend I noticed she has little scabs and raw spots inside her back legs, up next to her bag/teats. At first I tried Corona ointment, but she rolled in her sand paddock and the next day I had a horrible, crusty mess I had to wash off. Awful! Monday I tried MTG (Mand Tail Groom) and so far it seems to have made a difference. I too have thought of the Ani-hist products, but haven't gone that route yet. If MTG doesn't continue to work, I think I'll try the ACV or other suggestions here.

That is so wonderful you found a solution for your poor mare.  Morgans are so lovely.  It must have been heartrending to see that mane get rubbed out.  Sounds very sensible to me to help her immune system fight off the allergic reactions rather than just treat it topically.  She sounds very sensitive and must need more than just meds on the itches. 

My mare also had scabs and sores on her belly.  I refuse to give Antihistamines or steriods because of the risk of founder that is why I chose to do it in a more natural way.  I had tried the gooey pink fly ointment but she too got it all full of dirt when she rubbed her belly.  The immune builder seemed to be just what she needed.  I think the horses that have the allergies to the flies, noseeums, etc. perhaps have a lowered immune system.  My mare always seemed healthy and she has never been sick in the 22 years that I have had her.  The noseeums only seemed to come around to our area in the past 7 years or so.  They are horrendous when we are out gardening!  The immune builder is only used for a short time - they come off and go back on if needed.  It is an incredible product and I wish I had found it earlier rather than spend all the money on all the products that didn't work and now I have a happy horse!

Yes, I agree with you.  Those horses who have high sensitivity to insects of any kind must have a lowered immunity at least to that particular irritant, and an immune booster, especially all natural, makes a lot of sense.  I always avoid internal meds unless I really know they are necessary and there are no better options.  I think, too, that as horses age, just like us, they tend to have less  ability to fight off things that would not have bothered them when they were younger.  I have a 22 yr old gelding who is super sensitive to all sorts of meds, vaccinations, etc.  It is really challenging to know what to do with him sometimes.  Luckily, insects don't bother him as long as he has his fly mask and a good spray.  He has terrible reactions to vaccinations, and went into bad colics that last 2 times we tried it.  I have avoided them, with my vet's blessing but soon will have to think about trying at least some again.  So far his titers have been very good but it's been nearly 2 years now.  Glad your mare is so much better.  It is so awful to know they are are in discomfort when you are trying to help, and the things are not working!