A pharmaceutical composition for use in the treatment of skin inflammation in a mammal by topical administration, comprising a polyunsaturated fatty acid (PUFA) derivative, of formula, or a pharmaceutically acceptable salt, or solvate thereof, wherein - -Alk- is -(CH 2) 3 -[ cis]CH=CH-CH 2 -[ cis]CH=CH-CH 2 -[ cis]CH=CH-; - R 1 is a hydrogen atom; or R 1 is a C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 6 -C 10 aryl, 5- to 10-membered heteroaryl, C 3 -C 7 carbocyclyl or 5- to 10-membered heterocyclyl group; or R 1 is a group of formula -CH 2 -CH(OR 3)-CH 2 -(OR 4), wherein R 3 and R 4 are each independently hydrogen atoms or -(C=O)-R 6, wherein R 6 is an aliphatic group having from 3 to 29 carbon atoms; or R 1 is a group of formula -(CH 2 OCH 2) m OH, wherein m is an integer of from 1 to 200; and wherein - said alkyl, alkenyl, alkynyl and aliphatic groups are the same or different and are each unsubstituted or substituted with 1, 2 or 3 unsubstituted substituents which are the same or different and are selected from halogen atoms and C 1 -C 4 alkoxy, C 2 -C 4 alkenyloxy, C 1 -C 4 haloalkyl, C 2 -C 4 haloalkenyl, C 1 -C 4 haloalkoxy, C 2 -C 4 haloalkenyloxy, hydroxyl, -SR', and -NR'R" groups where R' and R" are the same or different and represent hydrogen or unsubstituted C 1- C 2 alkyl; - said aryl, heteroaryl, carbocyclyl and heterocyclyl groups are the same or different and are each unsubstituted or substituted by 1, 2, 3 or 4 unsubstituted substituents which are the same or different and are selected from halogen atoms, and cyano, nitro, C 1- C 4 alkyl, C 1- C 4 alkoxy, C 2- C 4 alkenyl, C 2- C 4 alkenyloxy, C 1- C 4 haloalkyl, C 2- C 4 haloalkenyl, C 1- C 4 haloalkoxy, C 2- C 4 haloalkenyloxy, hydroxyl, C 1 -C 4 hydroxyalkyl, -SR' and -NR'R" groups wherein each R' and R" is the same or different and represents hydrogen or unsubstituted C 1 -C 4 alkyl; and wherein the PUFA derivative is in the form of a racemate, a stereoisomer or a mixture of stereoisomers, wherein the PUFA is the sole active ingredient, wherein the skin inflammation is caused by atopic dermatitis, and wherein the amount of the PUFA is 1 wt% to 10 wt% of the pharmaceutical composition. - -Alk- is -(CH 2) 3 -[ cis]CH=CH-CH 2 -[ cis]CH=CH-CH 2 -[ cis]CH=CH-; - R 1 is a hydrogen atom; or R 1 is a C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 6 -C 10 aryl, 5- to 10-membered heteroaryl, C 3 -C 7 carbocyclyl or 5- to 10-membered heterocyclyl group; or R 1 is a group of formula -CH 2 -CH(OR 3)-CH 2 -(OR 4), wherein R 3 and R 4 are each independently hydrogen atoms or -(C=O)-R 6, wherein R 6 is an aliphatic group having from 3 to 29 carbon atoms; or R 1 is a group of formula -(CH 2 OCH 2) m OH, wherein m is an integer of from 1 to 200; and wherein - said alkyl, alkenyl, alkynyl and aliphatic groups are the same or different and are each unsubstituted or substituted with 1, 2 or 3 unsubstituted substituents which are the same or different and are selected from halogen atoms and C 1 -C 4 alkoxy, C 2 -C 4 alkenyloxy, C 1 -C 4 haloalkyl, C 2 -C 4 haloalkenyl, C 1 -C 4 haloalkoxy, C 2 -C 4 haloalkenyloxy, hydroxyl, -SR', and -NR'R" groups where R' and R" are the same or different and represent hydrogen or unsubstituted C 1- C 2 alkyl; - said aryl, heteroaryl, carbocyclyl and heterocyclyl groups are the same or different and are each unsubstituted or substituted by 1, 2, 3 or 4 unsubstituted substituents which are the same or different and are selected from halogen atoms, and cyano, nitro, C 1- C 4 alkyl, C 1- C 4 alkoxy, C 2- C 4 alkenyl, C 2- C 4 alkenyloxy, C 1- C 4 haloalkyl, C 2- C 4 haloalkenyl, C 1- C 4 haloalkoxy, C 2- C 4 haloalkenyloxy, hydroxyl, C 1 -C 4 hydroxyalkyl, -SR' and -NR'R" groups wherein each R' and R" is the same or different and represents hydrogen or unsubstituted C 1 -C 4 alkyl;