<e1>Pressure</e1> from shoes and walking cause <e2>friction</e2> and the body's natural response is to build up the skin to protect it from breaking down.
Pressure from shoes and
Pressure from shoes and walking cause friction and the body's natural response is to build up the skin to protect it from breaking down.
<triplet> Pressure <subject> friction <object> Cause-Effect(e1,e2)