It is an excellent herb to use for conditions involving excess mucus or phlegm such as asthma . It has bitter principles, saponins, which have a dissolving and loosening properties, which may explain why it has been used to dissolve thick or hardened mucus and aid in its expulsion from the body. It may help expel toxic waste from the lymphatic system as mucus secretions come from the lymphatic system.
Mucilage is also helpful in the digestive process.
Fennel - an aromatic herb, especially useful for stimulating the digestive process. It has a long history of use in helping to overcome colic, gas and other digestive disturbances. These oils appear to stimulate the lungs to eliminate phlegm. This is known as an expectorant action. Fennel also has diuretic properties.