Symptoms usually appear a few hours after exposure and peak at approximately eighteen to twenty-four hours.Other symptoms may include:

Malaise
Fever
Dyspnea
Flushed and/or discolored skin
Sweating
Small and fast inhalationsWithout proper treatment, pneumonitis may become chronic pneumonitis, resulting in fibrosis of the lungs and its effects:

Difficulty breathing
Food aversion
LethargyEnd-stage fibrosis and respiratory failure eventually lead to death in cases without proper management of chronic pneumonitis. Diagnosis
A chest X-ray or CT is necessary to differentiate between pneumonitis and pneumonia of an infectious etiology. Some degree of pulmonary fibrosis may be evident in a CT which is indicative of chronic pulmonary inflammatory processes. Diagnosis of Pneumonitis is often difficult as it depends on a high degree of clinical suspicion when evaluating a patient with a recent onset of a possible interstitial lung disease. In addition, interpreting pathologic and radiographic test results remains a challenge to clinicians. Pneumonitis is often difficult to recognize and discern from other interstitial lung diseases.Diagnostic procedures currently available include:

Evaluation of patient history and possible exposure to a known causative agent
High-Resolution Computed Tomography (HRCT) consistent with pneumonitis
Bronchoalveolar lavage with lymphocytosis
Lung biopsy consistent with pneumonitis histopathologyExposure to causative agents of pneumonitis in a specific environment can be confirmed through aero/microbiologic analysis to verify its presence. Subsequent testing of patient serum for evidence of serum specific IgG antibodies confirms patient exposure.Clinical tests include chest radiography or (HRCT) which may show centrilobular nodular and ground-glass opacities with air-trapping in the middle and upper lobes of the lungs. Fibrosis may also be evident.
If a large volume of nitrogen in the lungs is replaced with oxygen, the oxygen may subsequently be absorbed into the blood, reducing the volume of the alveoli, resulting in a form of alveolar collapse known as absorption atelectasis. Compression (relaxation) atelectasis
It is usually associated with accumulation of blood, fluid, or air within the pleural cavity, which mechanically collapses the lung. This is a frequent occurrence with pleural effusion, caused by congestive heart failure (CHF). Leakage of air into the pleural cavity (pneumothorax) also leads to compression atelectasis. Cicatrization (contraction) atelectasis
It occurs when either local or generalized fibrotic changes in the lung or pleura hamper expansion and increase elastic recoil during expiration. Causes include granulomatous disease, necrotising pneumonia and radiation fibrosis. Chronic atelectasis
Chronic atelectasis may take one of two forms—middle lobe syndrome or rounded atelectasis. Right middle lobe syndrome
In right middle lobe syndrome, the middle lobe of the right lung contracts, usually because of pressure on the bronchus from enlarged lymph glands and occasionally a tumor. The blocked, contracted lung may develop pneumonia that fails to resolve completely and leads to chronic inflammation, scarring, and bronchiectasis. Patchy atelectasis
Is due to lack of surfactant, as occurs in hyaline membrane disease of newborn or acute (adult) respiratory distress syndrome (ARDS). Rounded atelectasis
In rounded atelectasis (folded lung or Blesovsky syndrome), an outer portion of the lung slowly collapses as a result of scarring and shrinkage of the membrane layers covering the lungs (pleura), which would show as visceral pleural thickening and entrapment of lung tissue.