What should I do if I have pus under my fingernail and a swollen finger?

I’ve had a look at the picture, as well as had a dermatologist friend look at it. You should visit a doctor/dermatologist to have a skin scrape test (looking for fungus) and to find out a bit more history about the rash. It looks a bit scaly, so a fungus infection has to be ruled out. If it’s a fungal infection, it can be easily treated. Obviously, it could also be due to other common conditions, such as eczema and psoriasis, especially if it runs in your family or you had childhood eczema. It’s unfortunately a little difficult to tell as the photo is too close up.

Thank you for getting in touch with us. These brown lines are usually the result of pigments being deposited right below where the nail is growing. The medical term is melanonychia. There can be quite a long list of possible causes for this. But most of the time it is not something dangerous. You should check it out with your GP or skin specialist. What we would do is to take a close look at the nail and the skin around it with a "dermascope", or a good magnifying glass to advice you further. Take Care.