**Core Concept**
Dry skin due to excess dosage of datura is a manifestation of anticholinergic toxicity. Datura, a plant containing scopolamine and hyoscyamine, blocks the action of acetylcholine at muscarinic receptors, leading to various systemic effects.

**Why the Correct Answer is Right**
The absence of sweating is a direct consequence of muscarinic receptor blockade. In the absence of acetylcholine stimulation, sweat glands are unable to function, resulting in decreased sweating and giving rise to dry skin. This effect is mediated by the blockade of muscarinic receptors, specifically M2 and M3 subtypes, which are involved in the regulation of sweat gland function.

**Why Each Wrong Option is Incorrect**
**Option A:** Vasodilatation is not directly related to dry skin in the context of datura toxicity. While datura can cause vasodilatation due to its anticholinergic effects, this is not the primary reason for dry skin.

**Option C:** Central action refers to the effects of datura on the central nervous system, such as delirium, hallucinations, and confusion. While central effects are prominent in datura toxicity, they do not directly contribute to dry skin.

**Option D:** Change in BMR (Basal Metabolic Rate) is not a direct consequence of datura toxicity. While datura can affect various bodily functions, its primary effects on the skin are related to muscarinic receptor blockade, not changes in metabolism.

**Clinical Pearl / High-Yield Fact**
Datura toxicity is a classic example of an anticholinergic syndrome, which can also be caused by various other medications, such as antihistamines, antipsychotics, and certain antidepressants. Students should remember that anticholinergic toxicity can manifest with a range of symptoms, including dry skin, confusion, delirium, and tachycardia.

**✓ Correct Answer: B. Absence of sweating**