Sweat is readily visualized by a topical indicator such as iodinated starch (Minor test) or sodium alizarin sulphonate, both of which undergo a dramatic colour change when moistened by sweat. A thermoregulatory sweat test can evaluate the body’s response to a thermal stimulus by inducing sweating through a hot box ⁄ room, thermal blanket or exercise. Failure of the topical indicator to undergo a colour change during thermoregulatory sweat testing indicates hypohidrosis, and further tests may be required to localize the lesion.

Magnetic resonance imaging of the brain and ⁄ or spinal cord is the best modality for evaluation when the lesion is suspected to be localized to the central nervous system.

Skin biopsies are useful when anhidrosis occurs as part of a dermatological disorder. Biopsy results may reveal the sweat gland destruction, necrosis or fibrosis, in addition to the findings of the primary dermatological disorder.

Hypohidrosis is diminished sweating in response to appropriate stimuli. While hyperhidrosis is a socially troubling but benign condition, hypohidrosis can lead to hyperthermia, heat exhaustion, heat stroke and potentially death. An extreme case of hypohydrosis in which there is a complete absence of sweating and the skin is dry is termed anhidrosis.

Gustatory sweating or Frey's syndrome is another presentation of autonomic neuropathy. Gustatory sweating is brought on while eating, thinking or talking about food that produces a strong salivary stimulus. It is thought that ANS fibres to salivary glands have become connected in error with the sweat glands after nerve regeneration. Apart from sweating in the anhidriotic area of the body, it can produce flushing, goosebumps, drop of body temperature - vasoconstriction and paresthesia. Aberrant gustatory sweating follows up to 73% of surgical sympathectomies and is particularly common after bilateral procedures. Facial sweating during salivation has also been described in diabetes mellitus, cluster headache, following chorda tympani injury, and following facial herpes zoster.

Phantom sweating is another form of autonomic neuropathy. It can be observed in patients with nerve damage (following accidents), diabetes mellitus and as a result of sympathectomy. Phantom sweating is a sensation that one is sweating, while the skin remains dry. Sufferers can not distinguish whether it is real sweating or just a sensation. The phenomena is experienced in the anhidriotic, denervated area of the body, presenting an abnormal sympathetic nervous system function.

The symptoms of the inherited form of ichthyosis vulgaris are not usually present at birth but generally develop between 3 months and 5 years of age. The symptoms will often improve with age, although they may grow more severe again in old age.

The condition is not life-threatening; the impact on the patient, if it is a mild case, is generally restricted to mild itching and the social impact of having skin with an unusual appearance. People afflicted with mild cases have symptoms that include scaly patches on the shins, fine white scales on the forearms and upper arms, and rough palms. People with the mildest cases have no symptoms other than faint, tell-tale "mosaic lines" between the Achilles tendons and the calf muscles.

Severe cases, although rare, do exist. Severe cases entail the buildup of scales everywhere, with areas of the body that have a concentration of sweat glands being least affected. Areas where the skin rubs against each other, such as the armpits, the groin, and the "folded" areas of the elbow and knees, are less affected. When the buildup of scales is bad, the person with a severe case suffers from "prickly itch" when he or she needs to sweat but cannot because of the scales. Various topical treatments are available to "exfoliate" the scales. These include lotions that contain alpha-hydroxy acids.

Many people with severe ichthyosis have problems sweating due to the buildup of scales on the skin. This may lead to problems such as "prickly itch" or problems associated with overheating. The majority of people with vulgaris can sweat at least a little. Paradoxically this means most would be more comfortable living in a hot and humid climate. Sweating helps to shed scales which improves the appearance of the skin and prevents "prickly itch".

The dry skin will crack on digits or extremities and create bloody cuts. Skin is painful when inflamed and/or tight.

For children and adolescents: psychological precautions may include inconsistent self-image, mood fluctuates due to cyclical outbreaks, prone to addiction, may socially withdraw and/or separate when skin is noticeably infected, pre-occupation with appearance.

Strong air-conditioning and excessive consumption of alcohol can also increase the buildup of scales.

Over 50% of people with ichthyosis vulgaris suffer from some type of atopic disease such as allergies, eczema, or asthma. Another common condition associated with ichthyosis vulgaris is keratosis pilaris (small bumps mainly appearing on the back of the upper arms).

The burning heat is usually limited to the soles of the feet, but may extend up to the ankles or lower legs of some patients. The burning can sometimes be accompanied by feelings of 'pins and needles' or tingling in these regions. Nighttime is when almost all sufferers of this syndrome report the heat symptoms being the worst, with the condition getting better as morning comes. Those who have psychosomatic disorders sometimes display psychological symptoms along with the burning of feet associated with the syndrome. For most, there is no erythema of the skin of their feet during the heat sensations, and almost never is there accompanying tenderness along with it.

Idiopathic pure sudomotor failure (IPSF) is the most common cause of a rare disorder known as acquired idiopathic generalized anhidrosis (AIGA), a clinical syndrome characterized by generalized decrease or absence of sweating without other autonomic and somatic nervous dysfunctions and without persistent organic cutaneous lesions.

The term IPSF was first introduced in 1994 after researchers at Saitama Medical School speculated the primary lesion sites in patients were within cholinergic receptors of the sweat glands. The term IPSF represent a distinct subgroup of AIGA without sudomotor neuropathy or sweat gland failure.

Of people that have a sympathectomy, it is impossible to predict who will end up with a more severe version of this disorder, as there is no link to gender, age or weight. There is no test or screening process that would enable doctors to predict who is more susceptible.

Cholinergic urticaria (CU) is a type of physical urticaria (or "hives") that appears when a person is sweating.

CU typically presents with a number of small, short-lasting hives but may also involve cutaneous inflammation (wheals) and pain which develops usually in response to exercise, bathing, staying in a heated environment, or emotional stress. Although the symptoms subside rapidly, commonly within 1 hour, CU may significantly impair quality of life, especially in relation to sporting activities.

For a person to flush is to become markedly red in the face and often other areas of the skin, from various physiological conditions. Flushing is generally distinguished, despite a close physiological relation between them, from blushing, which is milder, generally restricted to the face, cheeks or ears, and generally assumed to reflect emotional stress, such as embarrassment, anger, or romantic stimulation. Flushing is also a cardinal symptom of carcinoid syndrome—the syndrome that results from hormones (often serotonin or histamine) being secreted into systemic circulation.

Commonly referred to as the sex flush, vasocongestion (increased blood flow) of the skin can occur during all four phases of the human sexual response cycle. Studies show that the sex flush occurs in approximately 50–75% of females and 25% of males, yet not consistently. The sex flush tends to occur more often under warmer conditions and may not appear at all under lower temperatures.

During the female sex flush, pinkish spots develop under the breasts, then spread to the breasts, torso, face, hands, soles of the feet, and possibly over the entire body. Vasocongestion is also responsible for the darkening of the clitoris and the walls of the vagina during sexual arousal. During the male sex flush, the coloration of the skin develops less consistently than in the female, but typically starts with the epigastrium (upper abdomen), spreads across the chest, then continues to the neck, face, forehead, back, and sometimes, shoulders and forearms.

The sex flush typically disappears soon after reaching orgasm, but in other cases it may take up to two hours or so, and sometimes intense sweating occurs simultaneously.

Burning feet syndrome can be inherited, or it can be caused by pressure being put on the nerves. Links also exist between this syndrome and diseases such as hypothyroidism, diabetes, and rheumatoid arthritis; links are also "believed" to exist between this syndrome and vitamin B (specifically pantothenic acid) deficiencies and renal failure.

It seems to be a small fiber neuropathy.

Sebaceous hyperplasia is a disorder of the sebaceous glands in which they become enlarged, producing flesh-colored or yellowish, shiny, often umbilicated bumps on the face. Newly formed nodules often swell with sweating (which is pathognomonic for the condition), but this diminishes over time.

Sebaceous glands are glands located within the skin and are responsible for secreting an oily substance named sebum. They are commonly associated with hair follicles but they can be found in hairless regions of the skin as well. Their secretion lubricates the skin, protecting it from drying out or becoming irritated.

Sebaceous hyperplasia generally affects newborns as well as middle-aged to elderly adults. The symptoms of this condition are 1–5 mm papules on the skin, mainly on the forehead, nose and cheeks, and seborrheic facial skin. The papules may be cauliflower-shaped. In infants, acne is sometimes associated with sebaceous hyperplasia.

Acquired idiopathic generalized anhidrosis (AIGA) is characterized by generalized absence of sweating without other autonomic and neurologic dysfunction.

AIGA is classified into 3 subgroups: idiopathic pure sudomotor failure (IPSF), sweat gland failure (SGF), and sudomotor neuropathy, with each subgroup presenting a different pathogenesis.

The most severe form of miliaria, "miliaria profunda", sometimes referred to as "wildfire" due to the rapid spread and severe burning sensations, generally occurs as a complication of repeated episodes of miliaria rubra. The obstruction is located deep in the structure of the sweat gland, causing the gland's secretions to leak between the superficial and deep layers of the skin. The rash, and associated symptoms, tend to appear within hours of an activity provoking sweating but similarly fade within hours when the stimulus for the sweating is removed. Miliaria profunda is characterised by non-pruritic, flesh-colored, deep-seated, whitish papules. The rash tends to be flesh-coloured as opposed to the prominent redness of miliaria rubra, and the risk of heat exhaustion is larger. Miliaria profunda is also less-commonly known as "Mammillaria"

The most commonly encountered form of the illness is "miliaria rubra", in which obstruction causes leakage of sweat into the deeper layers of the epidermis, provoking a local inflammatory reaction and giving rise to the typical appearance of redness (hence rubra) and larger (but still only a few millimetres), blister-like lesions. This form of the illness is often accompanied by the typical symptoms—intense itching or "pins and needles" with a lack of sweating (anhidrosis) to affected areas. There is a small risk of heat exhaustion due to inability to sweat if the rash affects a large proportion of the body's surface area or the sufferer continues to engage in heat-producing activity. Miliaria rubra is also known as "prickly heat" and "heat rash". Differential diagnosis should be used to rule out polycythemia vera, which is a rare hematological disorder and appears more often in males than females, generally not before the age of 40. Both disorders share the common denominator of appearing after taking a hot shower.

Idiopathic craniofacial erythema is a medical condition characterised by severe, uncontrollable, and frequently unprovoked, facial blushing.

Blushing can occur at any time and is frequently triggered by even mundane events, such as, talking to friends, paying for goods in a shop, asking for directions or even simply making eye contact with another person.

For many years, the cause of the condition was thought to be an anxiety problem, caused by a mental health disorder. However, in recent years experts in the field of the disorder believe it to be caused by an overactive sympathetic nervous system, an automatic response which sufferers have no mental control over. It is related to focal hyperhidrosis, more commonly known as excessive sweating, as it is caused by the same overactive nerves which cause excessive sweating. Sufferers of severe facial blushing commonly experience focal hyperhidrosis. Studies have also shown that patients with severe facial blushing or focal hyperhidrosis commonly have family members with one or both of the related disorders.

Acrocyanosis is characterized by peripheral cyanosis: persistent cyanosis of the hands or of the hands, feet, or face. The extremities often are cold and clammy and may exhibit some swelling (especially in the warmer weather). The palms and soles exhibit a wide range of sweating from moderately moist to profuse, but all peripheral pulses should have normal rate, rhythm, and quality. Exposure to cold temperatures worsens the cyanosis, while it often improves on warming. Aside from the color changes, patients normally are asymptomatic and therefore there is usually no associated pain. The most common sign, discoloration, usually is what prompts patients to seek medical care.

The most obvious sign that a person is suffering from pitted keratolysis is its classic appearance. The circular and shallow pits are the calling card of pitted keratolysis. The pits often overlap in places to produce larger areas of erosion. Occasionally these lesions present with a green or brown hue around and within the pits. These superficial erosions are found under the toes and on the soles of the feet, and especially at the pressure bearing points such as the heel. Both sides of the foot are usually equally effected. Pitted keratolysis is often linked to excessive sweating of the palms or soles (palmoplantar hyperhidrosis.) The bacterial digestion of the keratin results in a very foul odor, causing many of its sufferers great anxiety, especially in social situations. Thankfully, irritation is generally minimal, though occasionally burning, itching, and soreness are experienced with pitted keratolysis. The appearance of this condition’s characteristic lesions is much more pronounced when the affected area is wet.

Signs and symptoms include erythema (redness/flushing) and sweating in the cutaneous distribution of the auriculotemporal nerve, usually in response to gustatory stimuli. There is sometimes pain in the same area, often of a burning nature. Between attacks of pain there is sometimes numbness or other alterred sensations (anesthesia or paresthesia). This is sometimes termed "gustatory neuralgia".

Intracutaneous injection of pilocarpine (sweat gland stimulant) is known to evoke no sweat response, indicating that lesions are on the post-synaptic side of the nerve-sweat gland junction.

The proposed pathomechanisms of idiopathic pure sudomotor failure include:

- A deficit within muscarinic cholinergic receptors of the eccrine sweat glands.

- Interference in acetylcholine transmission to cholinergic receptors.

- A cross-reactive immune response which interferes with cholinergic transmission in the eccrine glands.

- Components of an immediate-type allergy (based on the dramatic resumption of axon reflex sweating following glucocorticoid treatment).

Acrocyanosis is persistent blue or cyanotic discoloration of the extremities, most commonly occurring in the hands, although it also occurs in the feet and distal parts of face.

The principal (primary) form of acrocyanosis is that of a benign cosmetic condition, sometimes caused by a relatively benign neurohormonal disorder. Regardless of its cause, the benign form typically does not require medical treatment. A medical emergency would ensue if the extremities experience prolonged periods of exposure to the cold, particularly in children and patients with poor general health. However, frostbite differs from acrocyanosis because pain (via thermal nociceptors) often accompanies the former condition, while the latter is very rarely associated with pain. There are also a number of other conditions that affect hands, feet, and parts of the face with associated skin color changes that need to be differentiated from acrocyanosis: Raynaud’s phenomenon, pernio, acrorygosis, erythromelalgia, blue finger syndrome. The diagnosis may be challenging in some cases, especially when these syndromes co-exist.

Acrocyanosis may be a sign of a more serious medical problem, such as connective tissue diseases and diseases associated with central cyanosis. Other causative conditions include infections, toxicities, antiphospholipid syndrome, cryoglobulinemia, neoplasms. In these cases, the observed cutaneous changes are known as "secondary acrocyanosis". They may have a less symmetric distribution and may be associated with pain and tissue loss.

Keratolysis exfoliativa, (also known as "Lamellar dyshidrosis,", "Recurrent focal palmar peeling," "Recurrent palmar peeling") is a sometimes harmless, sometimes painful skin condition that can affect the focal surface of the fingers and/or the palm or soles of the feet. It is often misdiagnosed as chronic contact dermatitis or psoriasis. It is characterized by dry skin and superficial, air-filled blisters. These blisters can be peeled off very easily and will leave reddish, tender areas. The loss of this horny layer of the skin, which protects the underlying layers, leaves the skin more vulnerable to dryness and cracking.

In most cases exfoliation resolves spontaneously and no lasting damage is seen. On the other hand, some patients experience cracking and even bleeding in extreme cases.