From the Instruction, "Relics in the Church: authenticity and preservation", December 2017
“Relics in the Church have always received particular veneration and attention because the body of the Blesseds and of the Saints, destined for the resurrection, has been on earth the living temple of the Holy Spirit and the instrument of their holiness, recognized by the Apostolic See through beatification and canonization. The relics of the Blesseds and of the Saints may not be displayed for the veneration of the faithful without a proper certificate of the ecclesiastical authority who guarantees their authenticity.
The body of the Blesseds and of the Saints or notable parts of the bodies themselves or the sum total of the ashes obtained by their cremation are traditionally considered significant relics. Diocesan Bishops, Eparchs, those equivalent to them in law and the Congregation for the Causes of the Saints reserve for these relics a special care and vigilance in order to assure their preservation and veneration and to avoid abuses. They are, therefore, preserved in properly sealed urns and are kept in places that guarantee their safety, respect their sacredness and encourage their cult.
Little fragments of the body of the Blesseds and of the Saints as well as objects that have come in direct contact with their person are considered non-significant relics. If possible, they must be preserved in sealed cases. They are, however, preserved and honoured with a religious spirit, avoiding every type of superstition and illicit trade.
A similar discipline is applied also to the mortal remains (exuviae) of the Servants of God and the Venerables, whose Causes of beatification and canonization are in progress. Until they are elevated to the honours of the altars through beatification or canonization, their mortal remains may not enjoy any public cult nor those privileges which are reserved only to the body of someone who has been beatified or canonized.”