Bhikha and Abdul Haq in “Tibb – Traditional Roots of Medicine in Modern Routes to Health” state,
“In spring, the warmer weather brings the formerly latent or dormant humoral excesses of winter up to the surface. Biologically, nature supports cleansing of the body in spring. In Winter, the digestive fire is high and people eat more sweet and heavy food. Most of the time, they aren’t able to assimilate these hard to digest food, and so the phlegmatic humour starts accumulating…"
"In Spring, the hardened phlegmatic humour begins to melt and the volume becomes great in the circulatory channels. As a result of the increased circulating phlegmatic humour, the digestive activity weakens, causing diseases. If you don’t assist these toxins moving out of the body, you become prone to many illness conditions e.g. allergies. Spring is the best time for detoxification because nature is already trying to clear out these toxins. A diet rich in light meals like soup with heating herbs and spices is encouraged to assist the body in the elimination of accumulated phlegmatic humour.”
Chishti in "The Traditional Healers Handbook" provides an excellent detox programme.