SELECT allergytype FROM Allergy_type GROUP BY allergytype ORDER BY count(*) ASC LIMIT 1
Which allergy type has least number of allergies?
[Schema (values) (types)]: | allergy_1 |  Allergy_Type : allergy (text) , allergytype (text) | Has_Allergy : stuid (text) , allergy (text) | Student : stuid (text) , lname (text) , fname (text) , age (number) , sex (text) , major (number) , advisor (text) , city_code (text);