Herbal teas are cleansing and, depending on individual varieties, often have medicinal properties. Nettle purifies the blood and makes the hair grow thicker, valerian root is a mild sedative and dandelion root is good for the digestion organs (digestion problems often show up on the skin).
I recommend loose leaves, roots, branches and flower buds instead of ready-made tea bags. The taste is fuller and you can mix different varieties according to your mood.
Buy the teas in see-through bags. Make sure none of the pieces have been squashed or pulverised and the colours should be vivid, not dull or musty looking.