I used to drink masses of coffee. It was always black, unsweetened and strong. I don't know how many mugs each day, probably about 8 or 10. I have never liked Ceylon tea and only occasionally drank hot chocolate, so it was coffee almost all of the time.
After dropping the fried and spicy food from my diet I needed to look for other culprits. My copious coffee was a logical one to investigate. I simply stopped drinking it for a week and observed the resulting improvement in my skin. Then I started drinking it again and saw the deterioration after a few days. I went through the same process again to confirm the result, then stopped drinking it completely.
Now I was left without a hot drink. Hot chocolate was too expensive to drink in quantities and I still hated Ceylon tea. I had to find an alternative. I searched the supermarket aisles for other drinks, which were not as numerous then as you see on the shelves now.
I tried cereal drinks but they were not very tasty. I gave them a chance for a couple of weeks but the taste did not grow on me. I made lemon verbena tea with leaves picked in my garden. That tea grew on me but still was not something that I wanted to drink more than one or two cups a day.
Eventually I settled on rooibos (red bush) tea. This is a South African herbal tea that is tasty, with a pleasant aroma as well. At first I drank it black (if a red liquid can be described as "black") but without milk I found that it gave me heartburn. I started to drink it with a small amount of 2% milk and that cured the problem.
Rooibos tea is very high in anti-oxidants, so it is a very healthy drink. I replaced my coffee of questionable health benefits with very healthy rooibos tea and watched my skin continue to improve.
I do occasionally have coffee, mostly if visiting someone or travelling and there is nothing else available. I no longer like it black and do appreciate the flavour with milk. When I remember I take a stash of rooibos teabags with me on a trip but they often come back with me unopened because I forget that I have them tucked away in a suitcase pocket somewhere. That is another reason why my skin normally deteriorates when I travel.