Following the example of Christ, the Church has always used bread and wine with water to celebrate the Lord’s Supper. (GIRM 319)
At Mass the Church uses only bread made from wheat, and wine made from the fruit of the grape-vine.
However many people have an allergy to gluten and are therefore unable to eat wheat bread.
The Church allows for the use of low-gluten hosts which are suitable for use by many people with gluten allergy. Those with gluten-allergy should always seek medical advice as to whether their level of allergy would permit the use of low-gluten hosts
Many people, also, have an intolerance of alcohol and are therefore unable to drink wine. This presents them with difficulty with regard to receiving Holy Communion.
The Church allows for the use of mustum in such circumstances.