Im a swimmer and for a long time practiced in a very warm, very chlorinated pool so the itching didn't seem un-normal when it started about 3 yrs ago. I quit that pool while still swimming. Starting about 2 years ago the AP ramped up to horrible; about a year ago to horrendous, when my wife found this site and I started taking Beta Alanine. It generally works really well, especially when I also chase it with a Gin & tonic. Some days are fine by comparison to others. I have noticed as few strange details about the AP.

If I swim, get out shower, towel dry and leave; its straight to Itch City.
If I swim, get out, air dry, I can them go about my business without discomfort or itchiness.
If I'm in the swim lane waiting for a set to start and someone rubs against my leg; In 5-10 min I'll be unable to concentrate on the Master workout, it itches that much.
If my wife wraps her legs around me; My legs itch for an hour afterward.
During a bad episode; The itching manifests itself more on the spots of skin damage (Actinic Keratosis) turning them very red, the itching isn't limited to those spots and on "normal" bouts there is no skin redness anywhere.
Type of soap doesn't matter
Hot showers are worse but it's incremental and a cold shower still causes the itchiness.(See above about toweling off)
Spa tub doesn't seem to bother me
Sauna doesn't seem to bother me.
Beta Alanine taken daily seems to help more and reduce the overall itchiness when it does happen, it requires another tablet.
Beta Alanine in tablets seems better than the powder form
Both forms take from 20-40 minutes to start feeling the tingling behind the ears which signals relief is eminent. It always seems to work top down, the legs are the last to stop itching.

My take away is there is definetly a pressure component to this, that i believe the simple act of toweling off is the proximate cause of. If i go for a run and then sit down on a chair: my legs will itch and If I lean back in that chair my back will itch, exactly the same as coming out of the shower. If i stood around until the sweat dried, I could sit down and not itch.

I am going to try Duplixent; and I'll let you know how it works out.