The Alum block has antiseptic properties that not only cool and refresh the skin after shaving but removes surface bacteria too. Using an Alum Block as an Antiperspirant - a Natural Deodorant An Alum Block is ideal for those who wish to use a natural antiperspirant. Applying an Alum Block to the underarms will give excellent odour and sweat protection an alcohol free antiperspirant. Alum Blocks are non-scented so you can still use your favourite scented deodorant. Alum Blocks can also be used as an all-natural treatment for oily complexions acne and pimples.