A study published in the Journal of
the Royal Society Interface reports that eyelashes divert airflow to
prevent drying of the eyes and protect against airborne
particulates.
Twenty two species of mammals possess eyelashes of a length
one-third the eye width. Wind tunnel experiments confirm that this
optimal eyelash length reduces both deposition of airborne particles
and evaporation of the tear film by a factor of two. This happens
because of the incoming flow's interactions with both the eye and
eyelashes.
Another study found that growth of eyelashes occurs in response to
exposure to allergens. Children with allergies have ten percent
longer and denser lashes than those without allergies. Allergens
trigger mast cells within the inside of the eyelid to release
prostaglandins that promote hair growth, which presumably protects
the eye. If models only knew their long lashes make them look
like they have allergies.