disadvantages of physical barriers

Hi, I hope this is useful, first year immunology coming in haha.

The main role of physical defences such as our skin and mucous membranes is to prevent the entry of pathogens. There are a few disadvantages of our body relying purely on these defences:

Limited effectiveness - if a pathogen is somehow able to bypass our skin, there is limited things the skin can do about it once it penetrates the barrier.
Slow response time - goblet cells in the skin can take time to react to presence of pathogens, for them to be effective they need time to synthesise mucus which will help protect our body from pathogens. This lag in response time could allow pathogens to enter the body before physical defences are fully mobilised.
Vulnerability - the skin is constantly exposed to the environment and hence is vulnerable to injury, a cut or abrasion can allow pathogens to enter the body.
Inability to recognise specific pathogens - physical defences are generally not able to distinguish between harmful and harmless bacteria, this means they may not be able to mount a targeted response to a particular pathogen.