Coming from the French term rache meaning “sore”, a skin rash can be defined as any skin eruption or lesion characterized by its deviation from the integument’s normal condition . This pertains to any change on the skin, affecting its texture, appearance, and hue . Known to some as skin lesions, these rashes may be classified according to their etiology, and furthermore, be differentiated based on their size, shape, consistency, patterns and distribution [3, 4].
Classification of Skin Rashes
1. Primary Lesions
These are physical changes in the skin directly attributed to trauma or disease.
Measuring less than 1 centimeter, macules are small and flat. They are usually distinguished due to their discoloration. No deviation from the normal skin thickness and texture visualized. Hence, they can only be appreciated by sight, not by touch. [5, 6, 7, 8]
The macules’ color changes may either be hypo or hyperpigmented. Hypopigmentation of the skin is mainly due to lack of the pigment melanin. Thus, areas of which are usually lighter in hue, as compared to one’s usual complexion. Examples of which are small vitiligo lesions. [9, 10]
Hypopigmented, light-colored macules less than 1cm in length seen in a patient with vitiligo.
Hyperpigmentation, on the other hand, may be brownish, bluish, whitish or reddish in hue. Macular brown lesions are often caused by the pigment melanin found in the epidermal layer of the skin. Blue pigmentation of the skin, on the other hand, is mainly attributed to the melanin found along the inner dermal layer. The reddish discoloration of the skin is brought about by dilatation of the blood vessels, with concurrent inflammation, present in the dermis. Café au lait spots exemplify such hyperpigmented lesions. [8, 10]
A picture of a patient with neurofibromatosis, with a macular café au lait spot, as seen with the red mark.
This skin lesion can be simple described as a bigger macule. Similar to the previous type of lesion, the patch is also flat, not palpable, and has color changes. But unlike the macule, this has a size of over 1 centimeter. These lesions can also be noted among patients with Vitiligo and Neurofibromatosis, as Café au lait spots. [11, 12, 13]
The image exhibits the difference between a macule and a patch. The macule (right) is smaller than the patch (left), which is more than a centimeter in diameter.
The photo shows a patch of hypopigmented skin, measuring a lesion more than 1 cm, in a patient with vitiligo.
This is an image of an infant with neurofibromatosis. Note the presence of a café au lait patch.
This is the image similar to that in the previous macule section, showing a patient with neurofibromatosis. Take note, this time, of the café au lait patch (encircled in blue). The patch is also hyperpigmented, but is larger than the macule in size.
A papule is a raised lesion, less than a centimeter in diameter. It can be seen as moles and even warts. This may also be combined with macules, as the maculopapular rash present among viral exanthems (eg. Measles). [3, 6, 10]
An image of a wart, Mollucum contagiosum, characterized as a papule less than 1 cm in size.
Maculopapular rash present in the Measles. Note the presence of non palpable macules and the elevated papules.
Simply put, plaques are coalesced papules. They are elevated and more than 1 centimeter in diameter. Eczema and Psoariasis are examples of skin disorders presented with plaques. [6, 10]
The image shows an eczema patient with numerous papules combined together forming a plaque.
This is a small fluid-filled skin lesion, measuring less than a centimeter in diameter. Note that the fluid inside this lesion is clear. Examples of which are found in herpes zoster. [3, 10]
A photo of a shingles patient, with small fluid filled vesicles.
Coming from the Latin term meaning “bubbles”, bullae are also skin lesions with clear fluid within. However, unlike the vesicles, they are larger, more than 1 centimeter in size. These are usually found among patients with bullous impetigo. [10, 14]
This image portrays a patient with bullae, fluid filled lesions. He is diagnosed with Bullous impetigo.
These are small skin lesions, red with inflammation, and filled with pus like fluid. They are usually seen as acne. 
Pustular lesions are seen as inflamed skin lesions, filled with pus. This was seen on this image, on a patient with acne.
This is an elevated lesion, measuring greater than a centimeter in diameter. It is palpable and, at times, circumscribed. It is composed of deep layers: the epidermis, dermis and the subcutaneous tissue. This is exemplified by erythema nodosum and lipoma. [5, 10]
This is an image depicting a nodule, palpable and with deeper area of involvement.
Cysts are fluid-filled nodules. They are raised and are more than a centimeter in diameter. Examples of which are sebaceous and epidermoid cysts. [6,10]
The photo shows an example of a cyst, sebaceous in type.
Otherwise known as hives, these are firm, pruritic and raised skin lesions which disappear after a short period of time. These may be seen among patients with allergic reaction and urticaria. [6, 10]
A patient with hypersensitivity reaction, presented with pruritic wheals.
These skin lesions are characterized by dilatation of blood vessels of the skin. It may happen in isolation or may be a part of an illness, like that in scleroderma. [3,6]
This photo represents an example of telangiectasia, showing superficial blood vessel dilatation.
2. Secondary Lesions
These skin lesions may progress from primary lesions, modified by injury, infection or other external factors. [10, 15]
These are dried primary fluid-filled lesions (either vesicles, bullae, or pustules) forming scabs and assortment of dried serum, debris and remnants of infection and inflammation. These can be seen among impetigo and psoriasis and [10, 15, 16]
An image showing a crusted skin lesion in a patient with psoriasis.
Resembling animal scales, these are dried exfoliations of the epidermis, the outer layer of the skin. These flakes are fragments of the stratum corneum rid off the skin. Examples of which are manifested in psoriasis and ichthyosis. [ 3, 15, 16]
Flaky, scale-like skin lesions seen in ichthyosis.
These are characterized by loss of epidermal layers brought about by pressure and friction. These are just minimal superficial losses. They usually heal without scars. [ 3, 10, 15]
The image shows an example of skin erosion, with layers of epidermis lost due to pressure.
These are sharp, well defined, cracks in the skin, involving the epidermis. They often occur in the cracks of the chapped lips and even the soles. [10, 15, 16]
An example of fissure located on the heels.
With loss of both the epidermal and dermal layers of the skin, these are irregularly shaped and are painful. They usually heal with scarring. They are caused by infection, tissue loss, and poor blood circulation. [10, 15, 16]
This image shows an example of a diabetic ulcer, irregular in shape, involving the epidermis and the dermis.
These are linear, superficial skin abrasions caused by either scratching or rubbing. If persistent, they can lead to formation of scars and depigmentation. They can be exemplified by simple scratch marks. [3, 10, 15, 16]
Excoriations of the skin resulting from persistent scratching of patient with atopic dermatitis.
This pertains to diffuse thickening of the skin, with concomitant accentuation of normal skin lines. It is also usually due to repeated scratching. [3, 10, 15]
This photo shows lichenification of an extremity brought about by repeated bouts of scratching.
These are new formations of connective tissue, depicting permanent fibrotic changes in the skin. This is usually due to dermal damage, and may commonly have visible depigmentation. [3, 16]
An image showing scar formation after damage was done to the dermis.
Diagnosing Skin Rashes
An accurate evaluation of a rash can be quite difficult. Its location, appearance and color can help make the diagnosis. But, thorough history and physical examination is still of utmost importance. Rashes can be a representation of a simple allergy or may even be a start of a very severe illness. Thus, it is of definite importance that when encountered with such rashes, a doctor’s consult must be immediately done.
Treatment for Scary Skin Encounters
Rashes are very unpredictable, can appear anywhere in the body. However, these can improve with gentle skin scare and avoidance of skin irritants. Hence, it may be important to remember the following [17, 18]:
- Use gentle cleansers for bathing.
- Avoid scratching, scrubbing or constant pressure on the skin.
- Do not apply any lotion, ointment or cream unless prescribed by the physician.
- Leave the affected area uncovered.
- Avoid the causative agent.
- Consult to doctor must be done.
3. Williams, G, et al. Primary Care Dermatology Module: Nomenclature of Skin Lesions. http://www.pediatrics.wisc.edu
8. Khan, A. Macule. http://www.healthline.com
10. Babu, H. What are Primary and Secondary Skin Rashes? 2010 Sept. http://www.suite101.com
12. Callen, J. Color Atlas of Dermatology. 2000. Philadelphia: WB Saunders.