Skin being the largest organ in human body, presents with many diseases on it. In fact, skin is the reflection of what is happening under the skin, or rather, inside the body. Most of the internal systems and organs in the body when get affected or dis-eased, they show their effects in the form of skin diseases, in various forms.
For example, when the immune system gets haywire, it shows on the skin in the form of diseases like psoriasis or lichen planus. When immune system gets hyper sensitive or delicate, it shows internal disease in the form of allergies such as urticaria or eczema.
When internal immune system is weakened, it gets impacted by external germs and there are various skin infections such as pyoderma, boils, carbuncles, warts, molluscum contagiosa, fungus infections, etc.
Similarly, when hormonal system inside gets sick, it can lead to some of the symptoms of hormonal diseases such as hair fall, alopecia areata, alopecia totalis, hyper-pigmentation, melasma, vitiligo, dry skin, and the like. Also, some of the genetic tendencies are displayed in the form of skin diseases, such as vitiligo, skin cancer, psoriasis, pemphigus, etc.
In other words, skin is like a mirror of our body, which reflects the internal changes, internal diseases. They need to be understood accordingly.
That means, the skin diseases are not skin deep; they are much deeper than the skin. They give us signal about the internal disease.