photoallergy

The story

1. Proto-Indo-European*bʰeh₂-
2. Proto-Indo-European*bʰéh₂os
3. Proto-Hellenic*pʰáwos
4. Ancient Greekφᾰ́ος (phắos)
5. Ancient Greekφῶς (phôs)
6. Ancient Greekφωτο- (phōto-)
7. Englishphoto-
8. Proto-Indo-European*h₂el-
9. Proto-Indo-European*h₂élyos
10. Proto-Hellenic*ál͏̌l͏̌os
11. Ancient Greekᾰ̓́λλος (ắllos)
12. Proto-Indo-European*werǵ-
13. Proto-Indo-European*wérǵom
14. Proto-Hellenic*wérgon
15. Ancient Greekἔργον (érgon)
16. GermanAllergie
17. Englishallergy
18. English todayphotoallergy

From photo- + allergy.