1. www.nhs.uk/conditions/asthma/
2. Peters SP, 'Asthma phenotypes: nonallergic (intrinsic) asthma', J Allergy Clin Immunol Pract. 2014 Nov-Dec;2(6):650-2.
3. Schatz M, Rosenwasser L. 'The allergic asthma phenotype', J Allergy Clin Immunol Pract. 2014 Nov-Dec;2(6):645-8