提供点理解，仅供参考。

1. Merriam-Webster's Dictionary of English Usage有这样的解释：

Look well and feel well tend to express good health. Look good does not generally refer to health, it relates to some aspect of appearance.This need not be personal appearance.

2. 国内陈敦金对“well”的解释似乎有些绝对：

good 和well都可以当形容词用在连系动词be,seem,look和feel之后，但语义不同。well只指“健康状况”。如：

She looks/seems/feels well. (healthy)

She looks good. (good appearance)

She feels good. (cheerful)

Those cakes look good/*well.

(Those cakes look as if they taste good.)

因为还有这样的说法，很有参考价值：

"That apple looks good."解释为"That looks like a good apple.",而"He looks good."解释为"He appears to be a good man."。look well一般用于指健康状况，如"He looks well."解释为"He looks healthy."或"He seems to be in good health."。look well也可以表示某人的外观或外表（appearance)，如"She looks well in that hat."解释为"She makes a favourable impression."

但是，well作为形容词描述外观这一说法，不少辞书没有收录。不过，在《韦氏大学英语词典》的well形容词词条，有这样的解释：

well adjective

pleasing or satisfactory in appearance

Our garden looks well.

Conrad Aiken

【1】look good 看起来很帅气 【侧重外表】

You do look good in black.你穿黑颜色的衣服确实很帅气。

【2】look well 看起来很健康【侧重健康】

You don't look well. You'd better go and see a doctor right away.  你脸色不好, 趁早去看看吧。

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