How health benefits of neem were found?
Neem is an evergreen plant abundantly present in India. However, Pakistan, Bangladesh, and Nepal are the other native places of Neem.  Centuries before Indian traditional medicinal systems including Ayurveda, Siddha, Unani, Amchi had recognized the medicinal value of neem. Almost 700 formulations of these medicinal systems are using neem as an active ingredient. The wide medicinal value of need gradually recognized by other countries also. China, USA, France, Germany, Italy have also formulated neem containing herbal and natural products. Nowadays, neem becomes a common ingredient of many therapeutic products used for preventive and curative purposes. In 1992, the US National Academy of Science published the report, titled as “Neem–A Tree of Solving Global Problem” has recognized the health benefits of the neem plants.
Phytochemical present in Neem
The scientific name of Neem is Azadirachta Indica, which belongs to the Meliaceae family. Herbal plant researchers are curious to know about the secrete of the medicinal value of neem. Researchers evaluated the biochemical constituents of neem and identified a complex combination of bioactive compounds like Azadirachta, nimbolide, nimbidin, Nimbin, and limonoids. It was expected that this combination of phytochemicals effective to treat multiple diseases. Moreover, a purified form of polyphenolic flavonoids, such as Quercetin and ß-sitosterol was the first isolated from fresh neem leaf. Both of these compounds are well established due to their natural antifungal and antibacterial properties.
What is the Mode of action of Neem followed to prevent and cure diseases?
The exact mode of action of neem is still not completely understood. But the combination of unique phytochemicals and antioxidant property of neem may provide a wide range of disease prevention and curing ability.
Antimicrobial property of neem is significant due to it inhibits microbial growth by potentiality breaking down of the cell wall. In-vitro research findings reported the antibacterial property of neem is effective against Staphylococcus aureus and MRSA.
Regular wear and tear due to physical and mental exhaustion and exposure to chemicals and pollutants increase oxidative stress and induce different diseases. The antioxidant property of neem has potent to scavenging the free radicals and reduce oxidative stress in the different tissue structure. Nimbolide and Azadirachta are two phytochemicals present neem have the greatest antioxidant property.
The anti-inflammatory property of neem obtains due to the regulatory effect against proinflammatory enzyme activities.
Neem induces angiogenesis (cell death) and can modulate tumor suppressor gene activities, both of these activities provide cancer-preventive activity. 
Different Forms of Neem
Every part of the neem plant has some therapeutic benefits and widely used for different purposes. Following are detail description of different forms of neem:
Benefits of Neem Bark
In India, neem bark is used as a natural toothbrush. Much Indian chew neem bark to strengthen their gum and whiten their teeth. Antimicrobial property of neem able to prevent oral infection. The neem twig prevents oral plaque formation.  Neem bark has cooling, astringent, bitter properties, which used to treat loss of appetite, intestinal worm formation, cough. 
Benefits of Neem leaves
Neem leaf has great blood purifying property. It is effective to treat insect bites as it helps to remove toxins from the blood. It is a useful antioxidant. The analgesic and anti-inflammatory properties of neem leaf reduce neuro-muscular pain. There are several health benefits of neem leaves as it can be used in multiple forms. The neem leaves can be used to make tea or juice. The neem leaves are boiled in water to make tea to get benefits of neem leaf tea. The neem leaves are bitter but due to benefits of neem leaves juice, it is used to improve metabolism and blood glucose.
Benefits of Neem fruit
Anthelmintic, antihemorrhodial, bitter, and purgative effect of Neem fruit also has great therapeutic value. 
Benefits of Neem flowers
It is useful for balancing body temperature. It helps to treat coughing by reducing respiratory mucus accumulation. This is a non-toxic and natural anthelmintic and astringent also. Neem seeds
Gedunin and Azadirachta are two phytochemicals present in neem seeds give antioxidant property. Neem seeds are also well known for their anthelmintic, antileprotic, anti-poisonous property. Both neem seed and fruit have antimalarial activity. 
Benefits of Neem oil
Neem oil has a great medicinal property and widely used in herbal formulations used against skin diseases. It has potent bitter and anthelmintic properties. Neem oil has anti-dandruff and anti-lice benefits. It also prevents the greying of hair and baldness. 
Benefits of Neem powder
Dried neem leaf is crushed and prepared a powder. There are several health benefits of neem powder. Mix one teaspoon of this powder with equal quality of clarified butter and honey to control skin allergy. Similarly, neem seed powder mix with rock salt and alum helps to maintain tooth and gum health. There are benefits of neem powder for face and skin. A teaspoon of dried neem leaf powder mixed with the same quantity of ghee (clarified butter) and honey was known to help control skin allergies.
Blending of different neem parts such as root, fruit, bark, flower, and leaves useful for blood diseases. External application of the paste of this blend help to treat many skin diseases like itching, burning sensation, wound healing.