A compound of formula I,wherein- X represents (CH2)n O, (CH2)n S or C2 alkylene;n represents 1 or 2; Ar1 represents indanyl, tetrahydronaphthyl, naphthyl or phenyl, which latter two groups may be substituted by one or more substituents selected from chloro, fluoro, OR1, O(CH2)m CONR20R21, C(O)R2, C1-6 alkyl (optionally substituted by one or more fluorine atoms), pyridyl, thiazinyl, phenyl or C7-9 alkylphenyl which latter two groups are optionally substituted by one or more substituent selected from halo, nitro, OR3, C1-6 alkyl (optionally substituted by one or more fluorine atoms), C(O)R4, C(O)OR5, C(O)N(R6)R7, CN, CH2OR14, CH2NR15R16, N(R8)R9, N(R10)SO2R11, N(R12)C(O)R13, OC(O)R19 and SO2NR17R18; m represents an integer 1 to 3; R1, R2 and R3 independently represent H, C1-10 alkyl (optionally substituted by one or more fluorine atoms), C7-9 alkylphenyl or phenyl, which latter group is optionally substituted by hydroxy; and R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, R15, R16, R17, R18, R19, R20 and R21 independently represent H, C1-6 alkyl (optionally substituted by one or more fluorine atoms) or phenyl; in which any alkyl group present may be interrupted by one or more oxygen atoms; provided that when X represents CH2CH2, Ar1 may not represent phenyl or phenyl substituted with one or more substituents OR1, in which R1 represents C1-10 alkyl; or a pharmaceutically acceptable derivative thereof, may be used for the treatment of a reversible obstructive airways disease or allergic conditions of the skin, nose and eye