The primary objective is to assess the concentration of Blomia tropicalis allergenic extract that induces a wheal of size equivalent to that produced by a 10 mg/mL histamine dihydrochloride solution, in order to be used as in-house reference preparation (IHRP).

The trial will consist of a single visit, in which the following procedures will be carried out:

• Demographic data (age, race, and gender).
• Clinical history.
• Inclusion/exclusion criteria.
• Physical examination (cardiovascular, pulmonary, neurobiological, gastrointestinal, dermatological, other body systems and height, weight).
• Pregnancy test.
• Performance of prick-tests (3 concentrations of of Blomia tropicalis extract, positive control, and negative control).
• Collection of blood sample (10 mL) from the patient to create a pool of sera for in vitro standardization of the allergen extract.

Each serum sample will be labeled with the subject's number and frozen. These serum samples will remain in the freezer until the study concludes. Once the study is complete, they will be transported to the sponsor's facilities, where all sera will be pooled. This serum pool will be used for additional in vitro tests necessary to standardize and characterize the extract and produce its corresponding In-House Reference Product (IHRP), as indicated by the Spanish Pharmacopeia and the European Pharmacopeia. Additionally, it will be used in the necessary in vitro analyses for the standardization of new batches of the allergenic extract. After the serum pool is formed, the tubes containing the original serum samples are destroyed.

- Assessment of adverse events during the 72 hours following skin testing.

Inclusion Criteria:

1. Female or male aged 18 to 64 years, both included.
2. Subjects who have signed and dated the informed consent form.
3. Subjects must reside in a geographical area where allergic problems caused by Blomia tropicalis are relevant.
4. Positive medical history of inhalant allergy (rhinitis and/or rhinoconjunctivitis and/or asthma) to Blomia tropicalis
5. A positive prick-test (mean wheal diameter ≥ 3 mm) with an extract of the same allergen and/or presence of specific IgE against complete extract or any molecular component to the allergenic source.
6. The area of the wheal obtained with 10 mg/mL histamine dihydrochloride should be ≥ 7 mm², which corresponds to a mean wheal diameter ≥ 3 mm.
7. The area of the wheal obtained with negative control should be < 7 mm², which corresponds to a mean wheal diameter < 3 mm.
8. Women of childbearing age (i.e following menarche and until postmenopause, defined as no menses for 12 months without an alternative medical cause, or non-subject to permanent sterilization methods, such as hysterectomy, bilateral salpingectomy and bilateral oophorectomy) must present a negative urine pregnancy test at the time of enrollment in the trial, as well as a confirmed menstrual period.
9. Women of childbearing age must commit to using a highly effective and adequate contraception method during the trial and up to 72 hours after the end of treatment with the investigational medicinal product. Such methods include combined (estrogen and progestogen containing) hormonal; contraception associated with inhibition of ovulation (oral, intravaginal or transdermal), progestogen-only hormonal contraception associated with inhibition of ovulation (oral, injectable or implantable), intrauterine device (IUD), intrauterine hormone-releasing system (IUS), bilateral tubal occlusion, vasectomized partner or sexual abstinence.

Exclusion Criteria:

1. Subjects outside the age range.
2. Subjects who have previously received immunotherapy within the last 5 years for the treatment of asthma or allergic rhinoconjunctivitis induced by allergens that may interfere with Blomia tropicalis extract.
3. Subjects with significant symptoms of rhinoconjunctivitis and/or bronchial asthma in whom discontinuation of systemic antihistamine treatment is contraindicated.
4. Subjects who have previously exhibited a severe adverse reaction during diagnostic skin prick tests.
5. Subjects on treatment with ß-blockers.
6. Use of drugs that could interfere with skin prick test reactions (e.g., antihistamines) (See Section 5.2).
7. Clinically unstable subjects (acute asthma, febrile, etc.).
8. Subjects with active urticaria lesions, severe active dermographism, severe atopic dermatitis, sunburn, eczema, psoriasis lesions in the area where the prick test is performed (risk of false positives).
9. Subjects with active herpes simplex viral infection, or herpes varicella zoster in the area where the prick test is performed.
10. Subjects with any pathology in which the administration of adrenaline is contraindicated (hyperthyroidism, hypertension, heart disease, etc.).
11. States in which the subject is unable to offer cooperation and severe psychiatric disorders.
12. Pregnant or potentially pregnant women and breastfeeding women.
13. Subjects with known phenol allergy.