Pallor is a pale color of the skin that can be caused by illness, emotional shock or stress, stimulant use, or anemia, and is the result of a reduced amount of oxyhaemoglobin and may also be visible as pallor of the conjunctivae of the eyes on physical examination. Pallor is more evident on the face and palms. It can develop suddenly or gradually, depending on the cause. It is not usually clinically significant unless it is accompanied by a general pallor (pale lips, tongue, palms, mouth and other regions with mucous membranes). It is distinguished from similar presentations such as hypopigmentation (lack or loss of skin pigment) or simply a fair complexion. Causes
migraine attack or headache
excess estradiol and/or estrone
osteoporosis
emotional response, due to fear, embarrassment, grief, rage
anorexia
anemia, due to blood loss, poor nutrition, or underlying disease such as sickle cell anemia
iron deficiency
vitamin B12 deficiency
shock, a medical emergency caused by illness or injury
acute compartment syndrome
frostbite
common cold
cancer
hypoglycaemia
bradycardia
panic attack
medications
ketorolac
amphetamines
ethanol
cannabis
lead poisoning
motion sickness
heart disease
Peripheral vascular disease
hypothyroidism
hypopituitarism
scurvy
tuberculosis
sleep deprivation
pheochromocytoma
squeamishness
visceral larva migrans
Orthostatic hypotension
methyldopa
loss of appetite
Space adaptation syndrome
fibromyalgia
Buergers disease
Hypovolemia

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Alcaftadine is used to prevent eye irritation brought on by allergic conjunctivitis. It is a H1 histamine receptor antagonist.It was approved by the U.S. Food and Drug Administration (FDA) in July 2010, under the trade name Lastacaft. Pharmacology
Alcaftadine is an antagonist at three of the histamine receptors (1, 2 and 4). The main indication for Alcaftadine is for prevention of allergic conjunctivitis. By blocking these three receptors, Alcaftadine has been shown to significantly reduce the effects of allergens. This effect on histamine receptors seems to show lower rates of itching, eosinophil recruitment and redness after exposure to an allergen. The effect of alcaftadine seemed to reduce the amount of eosinophil cells significantly as compared to olopatadine 0.1%. When animal models were used to test alcaftadine, alcaftadine 0.25% seemed to show superior results for decreasing E-cadherin expression as compared to placebo. The reduction of E-cadherin means decreased junctions which would lead to progression of allergic conjunctivitis. Clinical relevance
When Alcaftadine was tested against placebo and olopatadine, only Alcaftadine 0.25% was shown to have a clinically significant reduction in conjunctival redness scores 7 and 15 minutes after administration. When clinical groups where compared to placebo, treatment with all three of the alcaftadine groups (0.05, 0.1 and 0.25%) showed a reduction in secondary endpoints of (lid swelling, conjunctival redness, ocular itching/tearing) as compared to placebo. Adverse effects
In studies comparing the effectiveness of olopatadine to alcaftadine, there was not a dose response increase of adverse effects as alcaftadine doses increases for 0.05% to 0.1% to 0.25%.