Especially when it's cold and damp. Dampness bothers it the most, but Cold comes in a close second. TCM, like Western medicine, recognizes that checks and balances exist in the body. One of the checks and balances recognized in TCM is the Victor-Vanquished relationship. What this says it that each Element controls another.
Some people have imbalances in the Spleen because of problems in the Spleen.
Simply supplementing with Spleen-strenghten foods and herbs will help these people. End of problem. In these cases just giving Spleen-strengthening herbs and foods to the person is going to be like continuously bailing a leaky rowboat. You have to keep bailing until the leak is plugged. It's suppressing the Spleen, not allowing it to perform in tiptop shape.