It looks like cystic acne. Is it very tender and/or itchy? Big, fluid-filled ones which can be sort of moved about under the skin?
TMI pus warning
If so, he has my utmost sympathy. I had it for a number of years and it was awful. The itching when they were 'drying up' was horrendously intense, but id you scratched them or bashed them on something, they would weep. I had to throw clothes away from that. I have not had a back spot for a long time now, but the scarring is pigmented and pretty noticeable still.
Sorry if all this is TMI...it's such an awful condition. I found it useful to eliminate all showering and skin products containing sulphates. Shampoo was a key one for me, as I have long hair, and the cystic acne on my back was more or less in exactly the area where my hair falls when I am washing it! I use sulphate-free shampoos now. I will never know whether it was that that solved the problem, or whether the acne was on its way out anyway. I also had acne on my face (although not usually cystic acne, just the regular kind- don't know if it has a particular name!), and that also improved significantly within a similar timeframe- but I was taking some medication for that, so as you can see, it is difficult to pinpoint exactly which factors had the most impact. But definitely worth looking for sulphate-free products, as there are a lot more of them around these days. Basically they just don't foam as much as products containing sulphate.
He definitely needs to see a dermatologist, who will most likely suggest Roaccutane. This is, by all accounts, an absolutely amazing drug, and I know loads of people who have had acne permanently cured by it (or very long-term at any rate). It is a very powerful drug however, and has been known to affect fluids in various bodily orifices so can lead to some unpleasant side effects re dry eyes, dry mouth (and others!)
It also is not recommended for people with a history of any sort of mental health issues. I have had a number of bouts with anxiety and depression, so although I was offered the drug (and sorely tempted), I couldn't risk it.
Sorry for such a long post. I hope he finds some relief.