VAT ZERO RATE for goods and services to persons suffering from Alopecia (Totalis, Universalis or Areata), Post-Operative Hair Loss and Chemotherapy treatment, as permitted under GROUP 14 of Schedule 5 of the Value Added Tax Act 1983
If this applies to you simply enter the code 'VATZERORATE' once you get to the checkout and the VAT will be deducted.
However if you are unsure of your eligibility, you can also find more information on the GOV UK site. Some other useful reads, can be found on the Alopecia Forum and MacMillan Support. You can also find out more on the MacMillan forum.