Larsa Pippen is clapping back at haters criticizing her "excessive facial filler" ... revealing she recently had an allergic reaction to a treatment that made her face swell.

Check out the "Real Housewives of Miami" star's Insta clip from Saturday night -- she pushes back at people trashing a viral photo from her recent "Good Night New York" appearance, explaining ... "I did have PRP. I did have an allergic reaction to the PRP which I didn't even know you can have. So my face is a bit swollen but it doesn't look like that." Getty

BTW, PRP is a treatment that involves doctors processing one's own blood "to concentrate the number of platelets in the plasma" and then injecting it back into the person's face, per Cleveland Clinic . Its purpose is to stimulate collagen production a

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