A red swelling initially hurts (5)
I believe the answer is:
Here is my best explanation:
'hurts' is the definition.
('ache' can be a synonym of 'hurt')
'a red swelling initially' is the subsidiary indication.
'red' becomes 'che' (Che Guevara the Marxist revolutionary).
'initially' indicates taking the first letters.
The first letter of 'swelling' is 's'.
(Other definitions for aches that I've seen before include "discomfort", "Hurts; yearns", "sign of suffering", "Persistent pains", "Dull persistent pains", "Pains, hurts", "Gives a dull pain", "Dull prolonged pains", "Constant pains" and "Continuous pains".)