The Hands - A Special Case
Because of their role and function as human tools, the hands are particularly exposed to exogenous factors in the course of daily work in the house, office and garden. Because of this, the skin of the hands is markedly different from the skin of the other body areas. The skin of the palms is, again, completely different from that of the back of the hands.
When we look at the back of the hand, it is obvious that the skin is especially thin. This is because the subcutis has hardly any fatty tissue. In contrast, the palms (palmus manus) and especially the balls of the thumbs are well padded with tissue insensitive to pressure. Here, the subcutaneous fatty tissue (i) is especially thick and rich in fatty and connective tissue.
Characteristics of the hands
Physiological features as endogenous influencing factors
The lack of hair on the palms means there is also a lack of lipid-providing and moisture-binding sebum. On the back of the hands, which has only a few fine hairs, the density of sebaceous glands (i) is also much lower than on other parts of the body. The hands are consequently less protected from external influences, especially lipid-depleting ones.
Unlike the sebaceous glands (i), the sweat glands on the palms (i) show a higher density than in other skin areas. There is a shortage of some natural moisturizing factors (i) (NMF) and protecting lipids. In addition, the protective acid mantle (i) of the hands is deficient in important pH (i)-stabilizing, lipid-providing and moisture-binding components secreted by the sebaceous glands (i).
On the palms, the pronounced horny layer is rich in epidermal lipids, while on the back of the hands there is an undersupply of lipids due to the reduced density of sebaceous glands (i). The resulting weakened formation of the hydrolipid films means the hands dry out very rapidly when overtaxed. With frequent use of alkaline soaps, the pH (i) of the hands can quickly fall into a critical range.
Melanocytes and special features of the fingers
The typical pale reddish sheen of the palms and undersides of the fingers is due to the fact that they do not tan in response to sunlight. The reason for this is that the basal layer (stratum basale) of the inner hand surfaces contains no melanocytes, the pigment-forming cells. The palms and finger pads display especially prominent epithelial ridges. These projections, also known as cutaneous ridges, are responsible for an individual's fingerprints.
Exogenous influences on the hands
The - often daily - demands placed on the hands arise from:
- Washing with soap and water
- Exposure to alkaline and acidic substances
- Contact with solvents
- Damage from free radicals (i)
- Heat and cold
- Mechanical strain
Hand dermatitis and allergic reactions
Direct irritant and allergic contact dermatitis play a major role in diseases of the hands. They belong to the group of exogenous eczemas that are caused by external, damaging influences and substances (noxae (i)). Often the precursor to dermatitis is skin damage from an allergic reaction to a toxic irritant (also referred to as two-phase dermatitis).
If the skin and its barrier function are no longer able to regenerate properly due to a growing number of stress factors, an impaired barrier function can easily lead to the occurrence of sensitising reactions that cause contact dermatitis. Especially people with predisposing endogenous factors and an already dry skin should ensure when working at home or on the job (i) that the natural protection and regeneration mechanisms such as the barrier function and the base neutralizing capacity are maintained and supported by medical skincare products.