He hypothesized that by injecting people with hay fever with small amounts of a pollen "toxin", a state of immunity could be achieved.Allergen immunotherapy was part of mainstream medical practice for hay fever treatment in the 1930s. Society and culture
Sublingual immunotherapy drops are currently commercialized and used in most European and South American countries, and in Australia and Asian countries. In most European countries, national regulations allow marketing of allergen products as "named patient preparations" (NPPs). In the United States, drop formulations have not yet received FDA approval, though off-label prescription is becoming common. In 2014, the FDA approved a once-daily sublingual tablet containing allergen extracts for the treatment of "hay fever" (allergic rhinitis with or without conjunctivitis). Recognition by international agencies
The use of subcutaneous immunotherapy for treatment of environmental-based allergies and asthma is well supported by the majority of national and international allergy groups such as the World Allergy Organization, Canadian Society of Allergy and Immunology, European Academy of Allergy and Clinical Immunology, and the American Academy of Allergy, Asthma and Immunology. The use of sublingual immunotherapy is supported by few allergy agencies in order to allow for more investigation to occur on its practical use. Oral immunotherapy is generally not recommended, however the EAACI recommends that this treatment only be administered at specialized centres with expert professionals.Subcutaneous immunotherapy is both approved and regulated by the American Food and Drug Administration (FDA) and the European Medicinal Agency (EMEA).
Urea, also known as carbamide-containing cream, is used as a medication and applied to the skin to treat dryness and itching such as may occur in psoriasis, dermatitis, or ichthyosis. It may also be used to soften nails.In adults side  effects are generally few. It may occasionally cause skin irritation. Urea works in part by loosening dried skin. Preparations generally contain 5 to 50% urea.Urea containing creams have been used since the 1940s. It is on the World Health Organizations List of Essential Medicines. It is available over the counter. Medical uses
Urea cream is indicated for debridement and promotion of normal healing of skin areas with hyperkeratosis, particularly where healing is inhibited by local skin infection, skin necrosis, fibrinous or itching debris or eschar. Specific condition with hyperkeratosis where urea cream is useful include:

Dry skin and rough skin
Dermatitis
Psoriasis
Ichthyosis
Eczema
Keratosis
Keratoderma
Corns
Calluses
Damaged, ingrown and devitalized nails

Side effects
Common side effects of urea cream are:

Mild skin irritation
Temporary burning sensation
Stinging sensation
ItchingIn severe cases, there can be an allergic reaction with symptoms such as skin rash, urticaria, difficulty breathing and swelling of the mouth, face, lips, or tongue. Mechanism of action
Urea in low doses is a humectant while at high doses (above 20%) it causes breakdown of protein in the skin.Urea dissolves the intercellular matrix of the cells of the stratum corneum, promoting desquamation of scaly skin, eventually resulting in softening of hyperkeratotic areas. In nails, urea causes softening and eventually debridement of the nail plate. References
External links
"Urea". Drug Information Portal. U.S. National Library of Medicine.