Some saints such as Bernadette of Lourdes never turned to dust and bones.

 

Miracle?  Many would have you believe that it is a miracle, an act of God outside the norm.

 

Yet preserved bodies have always been around.  Sometimes dry hot sand preserved people. High radioactivity can do it.  Air and moisture being kept at bay can keep a corpse remarkably intact.

Moving them from their location can mean they will rot fast and smell terribly. The same thing happens bodies preserved deliberately. 

 

Religion has bodies that it says were not preserved accidently or deliberately.  The incorruptibles. 

Some of these miracle bodies are suspect for they ooze nice smelling oils decade after decade.  Interference is the most natural explanation.

 

God supposedly protected the body of Mary of Agreda to promote her insane book of revelations, The Mystical City of God.  This is actually an argument against the divinity of the phenomenon. 

Bernadette of Lourdes does have decay about the face and body and that is why a wax mask enhances her features.

 

St Agnes of Montepulciano who died in 1317 was later found incorrupt. Yet we are told that for a few centuries she remained like that until dampness invaded her tomb and caused a lot of decomposition.

The non-religious incorruptibles exist.  They are not mentioned.

 

Religion may use incorruptibles as signs and miracles but doesn't officially stake its authority on this claim.  It is more a permission to believe the miraculous is involved.  Its caution is understandable.  Oddities like this show that miracles are impossible in real life to identify.