Import rules for used clothing

Does anyone know what the requirements are if someone is sending used clothes to Spain?  A friend from the USA is sending some of my stuff over to me but has seen, on the USPS website, that the clothing needs a "certificate of disinfection" !!

I've never heard of this before and it's come as a bit of surprise.  When I moved here, I brought all my used clothes with me and didn't have any problems.  So can some enlightened soul advise me please?  Thank you.

 Think it may be to make sure there are no "bugs" on the clothes. When my daughter moved back to england from the Bahamas she had to have her stuff disenfected, but it was on pallets. 

Maybe the Bahamas has got more bugs than the UK then?  I'd like to know what the actual rules are though since I certainly didn't have my clothes disinfected when I moved here.

I've also had things sent from the UK, which were used items, and they didn't have any certificates either.

So, there's either a rule that only applies to certain countries or to all (and the Spanish customs ignores it !!!).   Anyone know or know where I can find out?  Thanks

 These are the US postal service requirements on "restricted" items.  It does say a certificate is required:

Restricted Items

Don't know if this is a US or Spanish requirement, though.  

There are also many restrictions on sending items the other way which is a US requirement.  One person on a site has said have them dry cleaned and put the receipt in the package and then write "disinfection certificate enclosed" on the outside of the package.