Hadith 2220

Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: There is no infection, no safar, no hama. A desert Arab said: Allah's Messenger, how is it that when the camel is in the sand it is like a deer-then a camel afflicted with scab mixes with it and it is affected by sub? He (the Holy Prophet) said: Who infected the first one?

Note: The majority of scholars interpret this to mean that these things in and of themselves do not transmit or cause harm through supernatural or hidden means but that Allah is ultimately in control and any fearful superstition around these is false.