Our lips, unlike other parts of our body, swell up very much

Any ant bite produces micro doses of envenomation, which contain lots of inflammatory substances, like vasoactive polypeptide, bradykinin, neurotrophilic polypeptidesserotonin, and many proteins which are highly allergic and capable of even producing anaphylactic shock.

When these polypetides or inflammatory kinins are liberated they cause intense vasodilatation, exudation of fluids in to the interstitial spaces, causing disruption of cell wall and swelling of cellular materials.

There is mitochondrial oedema. Cellular respiration would grind to a halt with these vasoactive amines. The anoxia of the cell produced by this oedema causes more swelling and destruction to the cell wall.

This phenomenon is happening in cells underneath the skin, but owing to the tough elastic layer underneath the skin , the swelling is moderate and not prominent.

This tough elastic skin is more, over the palm, sole, and body skin. But in areas like eye lids and lips there is only loose areolar tissue, which does not have any elastic property.

They are cavernous (hollow) loose connections of cells, because of their function. As lips have to modulate speech, feel the touch (the distance of even 1 mm between two sharp points can be identified by lips compared to body, where only 5 cm of distance between two sharp points can be identified.

Moreover, there are lots of free nerve endings, and plexus which are highly sensitive to touch in the lips.

These nerve endings when irritated after a sting, react violently, creating a local axon reflex sequelle of which is wheel (swelling), calor (change of color) rubor (redness) dolor (pain), which are called inflammatory responses to an injury, whether chemical or mechanical.

The same thing can happen over eye lids, prepuse of penis, and as well in female genitalia. The recrudence also would be very quick in these areas.