Nasal congestion is the blockage of nasal breathing usually due to membranes lining the nose becoming swollen from inflamed blood vessels. Background
In about 85% of cases, nasal congestion leads to  mouth breathing rather than nasal breathing. According to Jason Turowski, MD of the Cleveland Clinic, "we are designed to breathe through our noses from birth—its the way humans have evolved." This is referred to as "obligate nasal breathing. "Nasal congestion can interfere with hearing and speech. Significant congestion may interfere with sleep, cause snoring, and can be associated with sleep apnea or upper airway resistance syndrome. In children, nasal congestion from enlarged adenoids has caused chronic sleep apnea with insufficient oxygen levels and hypoxia, as well as right-sided heart failure. The problem usually resolves after surgery to remove the adenoids and tonsils, however the problem often relapses later in life due to craniofacial alterations from chronic nasal congestion. Causes
Allergies, like hay fever, allergic reaction to pollen or grass
Common cold or influenza
Rhinitis medicamentosa, a condition of rebound nasal congestion brought on by extended use of topical decongestants (e.g., oxymetazoline, phenylephrine, xylometazoline, and naphazoline nasal sprays)
Sinusitis or sinus infection
Narrow or collapsing nasal valve
Pregnancy may cause women to suffer from nasal congestion due to the increased amount of blood flowing through the body. Nasal polyps
Gastroesophageal reflux disease (theorized to cause chronic rhinosinusitis- the "airway reflux paradigm")
COVID-19

Nasal obstruction
Nasal obstruction characterized by insufficient airflow through the nose can be a subjective sensation or the result of objective pathology.
Pharmacological agents may also be required in cases where deficiency is more severe, in cases where iron loss exceeds dietary intake, and in individuals who follow a plant-based diet as non-heme sources often have lower bioavailability. When oral iron supplements are used, they should be taken on an empty stomach to increase absorption This might increase the risk of side effects however, such as nausea and epigastric pain. Anemia of Chronic Disease
Anemia of chronic disease (ACD) is the second most common cause of anemia after IDA. It usually occurs in individuals that have chronic inflammation due to a medical condition. Both diagnosis and treatment can be difficult as there may be an overlap with iron deficiency and thus it is a diagnosis of exclusion. Since ACD is caused by an underlying disorder, complete resolution of the condition is unlikely and we focus on controlling the inflammatory disorder rather than treating the ACD itself. Potential inflammatory conditions that can cause ACD are pulmonary tuberculosis, rheumatoid arthritis, and malignancies among many others. Thalassemia
Thalassemia is an inherited condition that has variants in alpha or beta globin genes that result in lower levels of globin chains required to make hemoglobin, resulting in alpha thalassemia or beta thalassemia, respectively. Diagnosis is made by DNA analysis for alpha thalassemia and hemoglobin analysis for beta thalassemia. Management of thalassemia involves chronic transfusions that maintain a hemoglobin level that reduces symptoms of anemia as well as suppresses extramedullary hematopoiesis which can lead to multiple morbidities.