system
Given the following post, respond as if you're commenting on Reddit:
human
Would taking anti-histamine drugs like cetirizine for allergies daily would make a person more susceptible in getting COVID-19?

Reasoning is that it slows down one's immune system response, which is important in evading coronavirus.
gpt
Anti-histamines don't slow the immune response, exactly.

Histamine has three major roles as far as immune response goes.

A) it increases local inflammation (which increases permeability of tissue to immune cells.)

B) signals to immune cells increasing chemotaxis - the movement of immune cells into the affected tissue.

C) increased nocireceotor activity (causing sensitivity, pain and itch). Designed to encourage you to stop using the area or move away from the cause.

Now while B is useful, it's an "all or nothing" response so hyper release of histamines doesn't provide benefit. C only affects symptoms. That means only A plays an ongoing role in immune function.

Now while that's useful, to a point, it also becomes inhibitory very quickly. Inflammation is a double edged blade, it helps the immune system a little, but if also damages tissues and organs - as an example, so called "long covid" is an example of chronic inflammation.

Anti histamines don't completely block the action of histamine, instead they mediate it. Slowing it down a little and limiting the ongoing activation of histamine receptors.

This means the important bits still happen, but the over-the-top extreme reaction is impeded and the consequences of that reaction are balanced out.

Ultimately, antihistamines may actually be of BENEFIT to covid by reducing some of the excess inflammation that can be caused by the disease as well as reducing symptoms like runny-nose, post nasal drip and excess respiratory secretions.